In the beginning of the film, we see that Charles (Hugh Grant), a confirmed British bachelor and serial monogamist, lives with his tone-deaf sister Scarlett (Charlotte Coleman) in London. The pair are habitually late to weddings (as we gather from remarks made by others at the wedding they attend late right now, which is the first wedding in the film). At the wedding, Charles meets Carrie, an American (Andie McDowell) and ends up spending the night with her. Also at the wedding, David (David Bower), the deaf younger brother of Charles and Scarlett, is targeted as an object of affection by a guest. We see that Fiona (Kristin Scott-Thomas) and Tom (James Fleet) are brother and sister and very wealthy and Gareth (Simon Callow) and Matthew (John Hannah) are a gay couple. We also briefly meet Bernard and Lydia who are at the wedding. Bernard (David Haig) likes Lydia (Sophie Thompson), but she dismisses him, saying that she is not as desperate as that. As the friends leave the wedding, we see Bernard and Lydia kissing passionately.
Charles ends up spending the night with Carrie and is surprised to see that she is leaving in the morning and returning back to America. The next thing we know, Charles and Scarlett are late again to wedding number 2 in the film, that of Bernard and Lydia. Father Gerald (Rowan Atkinson) officiates the service, his first, and seems to be unable to say the names of the bride and groom right and some other cues for added humor (Rowan needs no introduction of course).
Charles is elated to see Carrie at the wedding, until she introduces him to her fiance, a boorish, Scottish politician who is much older than she. To top things off, Charles is stuck at a table with four of his ex girlfriends. The girl who liked David introduces herself to him in faulty sign language and he is enchanted with her. Despite the fact she is engaged, Carrie sleeps with Charles again that evening after her fiance has gone off to Scotland. We now see that the two really care for one another.
The interim is when Charles receives an invitation to Carrie's wedding to Hamish Banks (Corin Redgrave) in Scotland. He goes to a very expensive store to choose a gift and meets Carrie. They spend a few hours shopping for her wedding dress and having a drink in a pub where Carrie reveals that she has had 33 lovers. After they part, Charles rushes off to tell Carrie that he loves her, but stops short. Instead, he refers to the "words of David Cassidy" which is the song "I Think I Love You." Carrie is affected, but kisses him on the cheek and moves on.
The next wedding is the third in the film and is that of Carrie and Hamish in Scotland. It is here where Scarlett meets a tall Texan named Chester (Randall Paul) who fancies her. Gareth tells everyone to find spouses for themselves. We find out that Fiona has been in love with Charles since she has known him and she reveals this to the stunned Charles and a table mate. Tragedy strikes when Gareth dies suddenly, presumably of a heart attack, at the wedding.
Now is time for the funeral - that of Gareth. Matthew gives the eulogy, which is the poem "Funeral Blues" by WH Auden. Carrie attends the funeral and sees Charles. Charles and Tom end up talking and Tom says that he is not waiting for the lightening bolt to hit, he just wants to meet someone and settle down.
We then see an invitation for the fourth wedding, Charles and xxxx. The audience does not know that he will be marrying Henrietta, his slightly wacky ex-girlfriend who was at weddings 2 and 3. The friends get to the wedding where Tom meets his distant relative while seating the guests and feels "the thunderbolt." Carrie appears at the wedding and tells Charles that she is separated from Hamish and that their timing has been very bad. Charles does not know what to do - he loves Carrie but is now committed to marrying Henrietta (Anna Chancellor).
David, who now is very steady with the young lady who learned sign language is at the wedding along with Scarlet and Chester. When Charles stays in the back of the church and asks Tom to delay the wedding, David wants to know what is going on. He tells Charles that he has three choices - he can go on with the wedding or tell everyone that the wedding is off. He says he can't think of number three.
Charles stands with Henrietta to get married and when the priest asks for objections, David comes up with the third idea. He objects to the wedding. He asks Charles to translate for him and says that the groom loves someone else. When the priest asks if he does love someone else, Charles answers "I do" and gets punched in the eye by the bride. Chaos erupts at the church.
The next scene is in the home of Charles and Scarlett with all the friends present. Carrie comes to the door and Charles, in the rain and outside, finally starts to let some of his feelings out. He asks her if she will agree "not to marry him" for the rest of their lives. Carrie answers "I do."
The song "Going To The Chapel" is then played as we see Henrietta marry a member of the guard, Scarlett marry Chester, David marry his girlfriend, Tom marry the distant relative, Matthew with a new partner (Duncan Kenworthy), Fiona marrying Prince Charles, and Charles and Carrie with their son, presumably not married.