The local fishing fleet of small boats from a small Cuban village comes in for the day. Most of the boats offload a few fish of small to medium size. After they put their gear and boats up for the night, and take the fish to the women for cleaning, the men head either for the bar or home. A young boy, Manolo (Alexis Cruz), runs to greet the old fisherman Santiago (Anthony Quinn) and helps him take down his sail. He tells Santiago he would like to go fishing with him again. Santiago tells him to stay with the "lucky" boat. The boy explains that it was his papa who made him leave and go with that other boat after Santiago was having trouble catching fish. The boy believes that Santiago's luck will return.
Tom Pruitt (Gary Cole), a journalist/writer, and his wife Mary (Patricia Clarkson) are having drinks at the open air bar (the Terrace) and watching the fishermen come in. Mary notes that the fishermen had a good catch. Lopez (Joe Santos), the manager of the bar, acknowledges that the weather has been good for some of the fishermen. He asks Tom Pruitt about his car. Pruitt says that a water pump had to be ordered and it should be in within a day or two, but he doesn't care if it ever comes. He likes it there and tells Lopez that their room on the second floor is just fine.
Manolo offers Santiago a beer on the terrace and Santiago says ok. He pauses and looks as four men go by carrying several fish on a board. Pruitt contemplates being a fisherman, telling his wife she could wait for him each day, with loads of children at her feet. She is not amused. Three other fishermen are having beers call out to Santiago, asking if he had any luck that day. He had not. One of the fishermen, Anderez (Paul Calderon) whispers to the others that Santiago is a curse on the village and will one day poison all their boats.
Manolo brings Santiago a beer and a Coke for himself. He asks Santiago if he can bring him some fresh bait sardines to him for tomorrow. Santiago says he already has sardines. Manolo wants to be of help in some way.
Anderez approaches Santiago and asks his opinion, as an acknowledged expert on professional baseball, what is wrong with Joe Dimaggio lately. Santiago explains that Dimaggio has a bone spur in his foot, so he's not quite himself. Anderez says it's his opinion that Dimaggio is old and his best days are behind him. He then notes how Santiago used to be the best fisherman in the entire area, but not anymore. He also mentions how Santiago was once a great arm-wrestling champion and he'd like the honor of engaging a great champion. One of the other fishermen calls Anderez a fool, but he persists. When Santiago invites him to sit down opposite him at the table, Anderez looks surprised, maybe even worried. He sits and they lock right hands. Manolo positions their grips, Anderez says, "Are you ready old man?" Santiago nods and they begin. Anderez goes for a quick win, but Santiago's arm doesn't budge. Anderez disingages and stands up, telling the others he made a mistake, that he's afraid he'd break Santiago's arm like a match stick, that the old man's arm is nothing but an old withered tree branch. Anderez orders beers for everyone and puts out a hand to shake with Santiago, but Santiago waves him off. Before walking off, he orders Santiago to not ruin them all with his bad luck. Manolo tells Santiago, "you would have won." Santiago replies, "not today."
As Manolo helps Santiago carry his gear to his small shack, the old man tells him he's going out far off shore tomorrow, that there's a fish out there waiting for him. Manolo warns him not to go too far, as he will be alone in a small boat. Manolo says he will ask his father to go out far too, so if Santiago needs help, they will be there. In response to concerns expressed by Manolo, Santiago says his eyes are still good and he thinks he's still strong enough to battle a big fish, and he also knows some "tricks." Santiago prepares to rest and read the day old newspaper that Lopez gave him. He wants to see how the Yankees and Joe Dimaggio are doing. Manolo offers to start a fire and go get him some food, but Santiago says he's fine. So, Manolo goes to get those fresh sardines that he'd earlier offered to get for bait. Santiago is asleep in his chair on the porch when his daughter, Angela (Valentina Quinn) drives over from Havana. She lights a lantern then puts a blanket around Santiago's shoulders. He wakes and she tells him she brought him some oranges and papaya. She tells him to bring his chair and come inside. He agrees, as long as she promises not to stay long. Angela knows that it's been 84 days since Santiago last caught a fish. She heard about it from Lopez' brother in Havana.
Angela tells Santiago that her and her husband (Thomas') tenant, Rodriguez, moved out and they have an extra room he is welcome to move into. She tries to convince him that God is telling him it is time to give up fishing. He disagrees and believes God will give him a fish, either tomorrow or the next day. Angela worries that he may die out on the water and the shame would be on her. Santiago tells her that there's no shame in a man dying the way he has lived. She begs him, telling him he's too old. He asks her to please let him be and let him continue fishing.
Manolo goes to see Lopez and tells him he'd like to buy some food. Lopez tells him what they have and the boy orders a little bit of each. Lopez, knowing the food is for Santiago, says, "and two beers?" Manolo says yes. Lopez tells Manolo he will put it on his tab and tells him he's a good boy.
Manolo takes the sardines, food and beer to Santiago. Santiago introduces him to Angela. She's abrupt to the courteous Manolo and prepares to go home, telling her father that if he changes his mind, she'll be back. Manolo tells Santiago that Lopez provided the food. Santiago says he'll have to get the belly of a big fish for Lopez. Manolo wants to hear about baseball, especially Joe Dimaggio. Santiago tells Manolo that Dimmagio's father was a fisherman, just like them. He then recalls the time when another baseball player, George "Sizzler" Sisler, came to the Terrace and Santiago wanted to ask him to go fishing with them, but he was too timid. Manolo remembered that Santiago asked him to ask Sisler, but Manolo was also too timid. They laughed about that.
After asking Santiago who was the best manager in baseball, he tells Santiago that he's the best fisherman there is. Santiago says he knows of some better, but Manolo says "there are many good fishermen, some great, but there is only you." Santiago thanks Manolo for saying that and told the boy that he makes him very happy. Manolo says good night and Santiago tells him he will wake him in the morning. Manolo says, "you are my alarm clock." Santiago says, "age is my alarm clock." Santiago dreams of the time when he was practicing with a fishing net, under the watchful eye of his tutor (presumably his father), who also reminds him to never forget that although they kill the fish to survive, they must always remember the beauty and courage of the fish, to appreciate them for their inherent natures. That dream seems to disturb the old man, as he wakes up looking distressed. At dawn the next day, Santiago goes to Manolo's house and wakes him up by throwing a papaya seed through the window at him. They head down to the shore and get the boat ready.
Tom Pruitt is up early and having coffee at the Terrace. Lopez engages him in conversation about his work. It's clear that Pruitt is having trouble writing anything of substance. Pruitt watches in obvious interest as Santiago and Manolo prepare the small boat to go out.
Manolo notices that Santiago has brought nothing with him to eat, but he assures the boy he's had enough for today. Manolo pushes the boat out and wishes Santiago good luck.
There are about nine boats going out, but Santiago the only one by himself. Pruitt asks Lopez if Santiago and the boy Manolo are related. Only "by affection" says Lopez.
As Santiago paddles out beyond the area where he'd been fishing for the past week, he talks out loud to himself, noting how to stay there another day would be a waste of time. He wonders when it was he started talking to himself out loud. He remembers singing out loud in the old days, so he does that for awhile. Santiago thinks that he started talking out loud to himself after the boy left him. He doesn't think he's crazy though, and he shouts out, "I don't care what anybody thinks!" He asks a sea bird if it would like to come ride with him, then decides that the bird also must not have any faith in him. He knows that a fisherman must have faith...and some luck...a lot of luck. He continues paddling.
Mary Pruitt walks out to the end of the boat pier, where Tom Pruitt is sitting with his note pad. He tells her he's making notes, but he can't tell her what will become of the notes. She observes he's been taking notes for a long time now. Tom changes the subject and talks about Santiago, who hasn't caught a fish for 84 days. Mary wonders if Santiago's doing something wrong. Tom says the people around there think Santiago is having bad luck. She says "that's one way to explain failure." Tom replies, "you're all heart." He promises to see about their car later that morning.
Santiago considers tying the fishing rope around his toe while sleeping and drifting, but he decides today is not a day for sleeping. For fishing poles, he has two curved tree branches, or thick bamboo shoots, with small ropes tied to them, extending from more rope coiled at the bottom of his boat. There are hooks and bait at the far end of the ropes, extending out into the water. Santiago notices a seabird flying over the water nearby and realizes it sees something. Suddenly the tip of one of his poles dips down. He sets the hook and pulls in a small bonita, or tuna, and thanks the bird. Later in the day, his pole tip jerks again and he carefully takes hold of the rope and waits. He's thinking it could be a marlin, given how far out from the beach he is, and maybe a big one. He asks the fish to please make a turn and to smell the sardines. Santiago is upset when he believes he's lost the fish, whatever it was, and he's in a state of despair, when there comes another tug on the rope. He asks the fish to not play games, to either eat the sardine or do not eat it. The line begins to tighten and Santiago pulls back hard, setting the hook. He wraps a coil of rope behind his back to take the pressure. The rope pulls taut and the boat begins to move, being pulled by this fish. Santiago considers tying the line to something in the boat, but he worries the fish would break it, so he continues to make use of his body and hands to hang on and provide give and take. He's grateful the fish is not diving down. He wishes he could see the fish, to know what he's up against.
The Pruitts' car is repaired and the mechanic tells Tom that it's a nice car and if he's interested, he knows someone who would probably buy it. Pruitt thinks about it briefly, then decides to sell it. Later, Mary is none too happy that he did that without first discussing it with her. She really wants to know what he's thinking, so she can better understand his motivations. He tells her he's thinking about the old man, about his not having caught a fish for 84 days, and how someone deals with something like that.
It's four hours until sunset. Santiago wonders if the fish will come up before that, or if it will come up with the moon. He calls out, "fish, I'm still strong, and you have the hook in your mouth." The rope pulls taught and Santiago falls down, as though the fish is showing him how strong it still is.
Pruitt is at the beach as the fishermen come in at the end of the day. He notices that Santiago does not return.
The tip of Santiago's other pole suddenly snaps off. He remarks how he doesn't have time for two fish, so he uses his knife to cut the rope on the second pole. He then decides to pull on the first rope a little to see if the fish will jump. The fish pulls hard and Santiago falls. His right hand is cut by the rope. Santiago wryly observes that it is now two rounds for the fish, none for him.
It's 2 a.m. and Tom Price is sitting by the window to his room. He can't sleep, thinking about Santiago still being out in his boat.
At dawn, Santiago wakes up, still holding the rope, and decides he should eat something. He cuts off a piece of the small fish he caught earlier. He wishes he had some salt and lime to put on the meat. He wishes the boy was there with him. He remembers back to a time when he directed Manolo to put some lime on some raw fish for them to eat, and Manolo said it was good. Santiago told him everything that comes out of the sea was good, except Portugese Man-O-War and sharks. That day on the beach, Manolo pestered Santiago to tell him again about the first time they went out fishing, when Manolo was five, and how Manolo nearly died because Santiago brought a big fish into the boat too soon and it thrashed wildly about until he killed it by clubbing it. Manolo asks Santiago what the biggest fish he ever caught was. He puts his arm way up high above him to indicate that it was nearly a 1,000 pound fish. Manolo is upset that he wasn't there with Santiago when he caught the fish, jealous that it was someone else.
Lopez is telling Tom Price how he was working in Havana ten years ago, bussing tables, when his cousin told him about the Terrace having a job available as a second barman. He went to the Terrace, took the job, and had been there ever since. Santiago was there then, alone even then, as his wife had died and his daughter was living in Havana. Lopez tells Tom that he likes Santiago and helps him during tough times, but because Santiago is so proud, he must do it indirectly, through Manolo. Tom expresses admiration for the dignity exhibited by Santiago in never giving up, even after 84 days. When he observes that Santiago had not come back the previous day, Lopez doesn't seem concerned. When Tom asks him if he cares about that, Lopez says it's all about respect for the way a man lives his life, which is more important than the man's life itself.
Santiago admits to the fish that he's a "little tired." He thinks the fish must be tired too, or else it's very strange. He would like the fish to know what kind of man he is. He says he would change places with the fish if he could. He encourages the fish to come up and face him, man-to-man. Santiago remembers his youth, when he could beat anyone at wrist wrestling. It was not whether he could win, but a matter of if and when he wanted to do it. He wants the fish to know that he had his mind made up and would stay with it until he dies if need be, and the fish would stay with him.
Mary Pruitt tells Tom she is on the verge of depression, that she's not feeling useful to herself or anyone else. He tells her he can't leave until he learns the outcome of the saga of Santiago.
Santiago's left hand cramps up and he talks to it, telling it to open up and help him. He bangs it against his leg. It loosens up just as the rope goes taut and the fish jumps high out of the water. He now knows it's a huge marlin, and when it makes several more jumps, Santiago pleads with it to please don't break the line. Santiago stumbles and hits the bridge of his nose on the bow, and the rope cuts his left hand. He tells the fish that it can't go deep again and he will show it how strong he is as he begins to work the line and bring the fish in. He tells the fish that he loves and respects him very much, but before the day ends, he will kill it. As the marlin tires and gets closer to the boat, Santiago can see just how huge it is. He encourages the fish not to do anything foolish and says, "my God, I wish the boy could be here to see this!" He puts the rope under his foot, picks up his harpoon and thrusts it into the side of the marlin. It thrashes wildly, rising up high out of the water and splashing water over Santiago, and then it dies. Santiago ties the marlin to the side of his boat and begins the long trip home. The rest of his fellow fishermen have long ago gone in from their day of fishing. Manolo is now officially worried. He's sitting on the edge of a beached boat and the Pruitts walk by and Tom asks if they can sit with him.
Tom asks Manolo if he and the old man are good friends. He says yes, that they've gone fishing together many times. Mary asks how old Santiago is and Manolo says he doesn't know, and that it doesn't matter. He says Santiago is a great fisherman. He tells the Pruitts about a fishing trip with Santiago where they caught a large fish, a female, and the male was with her and kept circling out of concern. Once Santiago had gaffed and killed the female, the male jumped high out of the water to see what had happened. That had made Santiago very sad, and as a result, Manolo was very sad. Pruitt asks Manolo if there's anything they can do and he tells them no, that Santiago will come back.
Santiago figures his fish weighs around 1,500 pounds, and would sell for 30 cents a pound. Santiago wonders if maybe it was a sin to kill the fish. He reminds himself that St. Peter was a fisherman and so was Dimaggio's father. Anyway, he loved the fish, so there was no sin. Then he chastises himself as having no understanding of what sin is.
That night, Manolo goes to Santiago's shack and looks around. He looks at the sports page of the paper and says, "please come back old man."
The Pruitts consider hiring a boat to go look for Santiago. They had already tried appealing to Lopez and the authorities, but they aren't that concerned. Everyone seems to realize that it would likely do no good and it isn't something they get all worked up about. Tom tells his wife that they'll just wait, and try to understand.
Santiago is making slow progress toward shore, humming to himself. He notices a fin in the water approaching fast. It's a mako shark, coming after some free marlin meat. Santiago thrusts his harpoon into the shark, but loses hold of the rope and the shark swims away with the rope and the harpoon. The shark had taken a bite of the marlin, releasing blood into the water. Santiago knows that will attract more sharks. Santiago fashions another spear using his knife and his fishing pole, tying the knife to one end of the pole. He remembers back to the day he married Maria. He took Maria down to his fishing boat and tells her that while he gave her his heart at their wedding, now he promises her to use his boat take fish from the sea, as long as he lives.
Manolo goes to the Terrace and asks to see the newspaper. Lopez tells him he can keep the paper. Lopez tells Tom Pruitt that the boy cannot read, that Santiago had taught him to read just the sports page, the baseball scores. Manolo runs out onto the pier and yells out to Santiago that the Yankees beat the Tigers, twice, and Dimaggio had five hits with two home runs. Angela had arrived and she approaches Manolo and tells him that Santiago can't hear him. The boy disagrees, telling her that all sounds remain in the air forever. Santiago told him that. She tells him that sound is lost when there's no one to hear it. Manolo doesn't argue about it anymore, but tells her that the old man is out there. She says, "maybe alive and maybe not." She wonders why foolish people like Manolo keep telling her father that he's a great fisherman, when he's old and shouldn't be doing that anymore. Manolo resents her for talking about Santiago that way. It's obvious he loves the old man, and considers him to be like a grandfather. Angela is worried that people will be forever critical of her for not taking proper car of her father in his old age. She said she tried and says in her next life, her father will be a tailor.
Several more sharks approach and Santaigo stands up with his new spear and prepares to do battle. They feed, he stabs, over and over, until the blade of the knife snaps off. He apologizes to the marlin and regrets having gone out so far, for both their sakes.
Mary wakes in the night and tells Tom that she dreamed a cruise liner picked up the old fisherman and gave him a big dinner. She goes back to bed, while Tom stays up, thinking and wondering.
On day three, Santiago drinks the last of the bottle of water he'd brought with him. He acknowledges being tired inside. More sharks come and Santiago hit at them with what's left of his fishing pole and his oar. He can't keep them from tearing great chunks out of the marlin.
It's Sunday and people are coming out of church. Manolo is on the beach, watching and waiting. He's the first to see Santiago's boat. He runs and tells Tom Pruitt, who was in his room. Tom wakes his wife and tells her. Angela goes down to the beach and watches, as do many of the other fishermen and people who'd gathered at the Terrace for coffee. They see the head and tail of the great marlin lashed to the side, with nothing but exposed bones in between. Manolo runs and helps Santiago take down his sail. Santiago tells Manolo that the sharks beat him. Manolo goes to help Santiago with the sail, but the old man tells him no. He wants to do it himself, as people are watching, but he's too tired and can't do it. He stumbles and falls. Angela and Manolo run towards him, but he gets back up and says he's fine. Angela calls him a stubborn old man and invites him to come see his grandchildren soon. Anderez calls out to Santiago, observing that he had caught a truly great fish and he's not bad luck anymore.
Next day, Manolo goes to see Santiago. He's sitting on the porch soaking his wounded hands. Manolo wants to go fishing with Santiago again, and continue learning. Manolo tells him he has another knife for Santiago. There's several days of bad weather expected, so there is time for the old man's hands to heal and Manolo to get the gear together and ready. Santiago tells Manolo that he missed him out there. He says it was a great loss (the fish), but a great gain (Manolo will be able to join him again). He tells Manolo that a man, or a fish, can be destroyed, but not defeated. Manolo wants to talk about the Yankees. He tells Santiago they won and Dimaggio's spur is gone, the operation worked. Santiago asks him if they can win the pennant and he says "of course, have faith in Dimaggio!" Santiago laughs and tells Manolo that now he's becoming like him.