Less than a week after getting married, Paul Blart (Kevin James) gets a notice of divorce since his wife was immediately disillusioned with marriage. To make things worse, his own mother gets hit by a milk truck. However, Paul takes comfort in his job as a mall cop. He is seen accompanying a little boy back to his mother. The mother thanks Paul and tells her son to hug him. The boy instead smacks Paul and runs off again.
Paul's daughter Maya (Raini Rodriguez) just got her acceptance letter to UCLA. Paul gets a letter inviting him to a security officers convention in Las Vegas. Thinking this could be something big for him, he announces this to Maya and invites her to join him. Not wanting to spoil his joy, she decides not to tell him about her acceptance just yet.
The two head off to Vegas and get accommodated at the Wynn Hotel. Paul meets the general manager, a pretty young woman named Divina (Daniella Alonso), though he believes she is making a pass at him, even though she is already seeing the hotel's head of security, Eduardo (Eduardo Verastegui). Maya becomes friends with the hotel's valet Lane (David Henrie). A fellow security guard named Donna (Loni Love) knows of Paul's saving of his mall and drops a hint that he may be the key note speaker that night for the other guards.
In the hotel, a criminal named Vincent (Neal McDonough) is plotting with his team to steal valuable artwork from the hotel. They disguise themselves as hotel staff members and plan out their heist.
Paul learns that another security guard, Manero (Nicholas Turturro) is giving the speech that night, crushing Paul's spirit. He also becomes too overprotective of Maya, spying on her as she talks to Lane. She sends him off after telling him that he's embarrassing her. Maya later goes out to the pool bar with Lane after telling her dad she was gonna take a bath. When he doesn't find her in there, he freaks out and calls the security to find Maya until she calls him from her phone. The guards leave with annoyance, and Eduardo mocks Paul's profession. Maya finds her dad at the cafe, and he says he found out about UCLA from the letter in Maya's bathrobe. He wants her to stay close to home at a junior college, but Maya gets angry and declares that she's going to UCLA.
Paul hangs out with Donna and three other guards - Saul (Gary Valentine), Khan (Shelley Desai), and Gino (Vic Dibitetto) - around the hotel to check out all the cool non-lethal equipment on display. Later, Paul finds Manero drunk as he tries to hit on a woman at the bar. While Paul attempts to diffuse the tension, Manero passes out, and Paul is then given the chance to be the speaker. He calls Maya to ask her to come by, but she is at a party with Lane.
As Paul gets ready to give his speech, he decides to get some fresh air, only to come across a wild bird and get into a fight with it. He then goes up to give the speech, while Vincent and his cohorts begin to pull off their heist. Maya ends up walking into their suite, and she is taken hostage. Lane goes looking for her and gets taken as well. Paul gives a rousing speech that moves all the other security guards, as well as Divina, who finds herself inexplicably attracted to Paul with each passing moment. Maya attempts to call Paul, only for him to ignore the calls during the speech. After it ends, Paul calls Maya and learns that Vincent has her. Paul runs to her, only for his hypoglycemia to act up and make him pass out. He gets back on his feet by catching drops of melted ice cream from a little girl's cone.
Paul springs into action and takes down a couple of Vincent's goons by sheer dumb luck. He learns what they're trying to steal and plans to stop them while also rescuing Maya and Lane. He gathers all the non-lethal equipment and takes out most of the goons. Meanwhile, Maya escapes the room she's in using the copper wire in a snow globe that Lane gave her to unlock the door. They have to go back to the room since the goons are too close. One goon offers Vincent an oatmeal cookie, but he rejects it since he is terribly allergic.
After taking out one goon carrying a Van Gogh painting, Paul contacts Vincent and tells him they'll trade the painting for Maya. Vincent drags Maya out after hearing her tell Lane about Paul's fear of being alone after being divorced, losing his mother, and now having his daughter go away to college. Vincent uses this against Paul, but it doesn't faze him as he got Donna, Saul, Khan, and Gino to join forces with him. They square off against all of Vincent's henchmen as he takes Maya and Lane to the helipad to get away. The security guards clumsily but successfully take out the villains.
Paul gets to the rooftop to see Vincent has taken Maya and Lane to the roof of another building. Eduardo goes up to find Paul. Paul thinks he is in on the scheme, but Eduardo is just mad that Paul has attracted Divina's attention. They settle their differences and, with the help of the other guards, including a now sober Manero, Paul uses a zipline to get to the other building and stop Vincent. He uses a gun with some sticky material to take out the remaining henchmen, but he accidentally gets his own feet stuck. Vincent is about to shoot Paul when Maya gets oatmeal lotion and rubs it all over Vincent's face, causing him to go blind and to swell out. Paul jumps out of his shoes and headbutts Vincent, knocking him out cold.
The villains are arrested and the artwork is returned safely. Paul makes peace with Eduardo and talks to Divina, who admits her attraction to Paul, but he feels that she must stay with Eduardo (especially since he's crying). She agrees, though Paul immediately realizes he just made a huge mistake. Later, the security guards honor Paul with a medal of valor. Finally, Paul decides that he must let Maya go and supports her choice to go to UCLA.
Months later, Paul drops Maya off at the UCLA campus with her new friends. Paul walks back to his car when he spots a policewoman riding a horse downtown. He tries to coolly walk over to her, but she starts to write him a ticket for jaywalking in a business district. He mentions that he's an officer, and the woman instead decides to give him her number. Paul then proudly smacks the horse on the rear, causing it to kick him against his car. The policewoman asks Paul if he's okay. He says he's never been better.