The story takes place in a single day during a lavish wedding that merges a nouveau riche Southern family with an established wealthy Chicago family having possible ties to organized crime.
Dino Corelli (Desi Arnaz Jr.) marries Muffin Brenner (Amy Stryker) in a lavish Episcopalian church wedding presided over by a doddering, forgetful bishop. The wedding party goes to the Corelli mansion for the reception. Bedridden matriarch Nettie Sloan (Lillian Gish), mother of Regina Sloan Corelli (Nina Van Pallandt) and grandmother of groom Dino, is being tended in her upstairs bedroom at the mansion by drunk, lecherous Dr. Jules Meecham (Howard Duff). While speaking with wedding planner Rita Billingsley (Geraldine Chaplin), Nettie suddenly dies. Dr. Meecham informs Dino's father Luigi Corelli (Vittorio Gassman) of Nettie's death, but Luigi is unable to tell his wife Regina because she is high on drugs and mentally unstable. Nettie's corpse remains in bed throughout the reception, while various attendees visit her room without realizing she's dead. By the time bossy daughter Toni (Dina Merrill) finds out and plans a dramatic announcement, other family members are mostly not surprised or even too upset.
The Brenners are a nouveau riche family from Louisville, Kentucky, where Muffin's father, "Snooks" Brenner (Paul Dooley), made millions in the trucking industry. Muffin and Dino met because his military academy was near the Brenner's estate. By contrast, the Corellis are an old money North Shore Chicago family via Regina's and Nettie's Sloan lineage. Luigi is rumored to have mob connections. Due to the family's questionable past, more than a hundred guests sent their regrets. Only one guest (other than family members) attends. Nevertheless, the imperious Rita is determined to run the reception by the book, setting up a receiving line for the one guest and then asking family members and staff to also go down the line so it won't look so empty.
A series of disasters unfold, including the display of an embarrassing nude life-size portrait of the bride (a gift from the groom's bohemian Great-aunt Bea); the caterer Ingrid Hellstrom (Viveca Lindfors) becoming ill, then getting high and causing a disturbance after Dr. Meecham gives her a pill; and a tornado blowing up just as the cake is about to be cut, forcing everyone to rush to shelter in the cellar. Two more guests arrive late, Tracy Farrell (Pam Dawber) and Wilson Briggs (Gavan O'Herlihy), the exes of the groom and bride, respectively. Wilson was supposed to be Dino's best man, but stood him up, possibly because Dino stole Muffin from him. Tracy and Wilson bond over their mutual anger.
The unsavory secrets of each family are revealed. Regina Corelli is a drug addict who needs regular injections just to stay functional. Her marriage was arranged by Nettie after Luigi met Regina while working as a waiter in Italy. Luigi was forced to change his name and be estranged from his Italian family for 22 years. His Italian-speaking brother unexpectedly shows up, making passes at all the women, but when Dr. Meecham reminds Luigi that Nettie is dead and can't impose the marriage conditions anymore, Luigi is thrilled to see his long-lost brother. Regina's sister Clarice has an ongoing scandalous romance with Randolph, the African-American family butler; her other sister Toni is married to Mack Goddard (Pat McCormick), who falls in love at first sight with Tulip Brenner (Carol Burnett), the mother of the bride. Mack spends the entire reception trying to secretly woo Tulip into agreeing to a tryst.
Snooks Brenner has a borderline incestuous attachment to his nearly mute daughter Buffy (Mia Farrow), the maid of honor, who speaks at the reception only once, to tell Dino she's pregnant and he is the father. Buffy behaves seductively towards men including her father, jealous of the attention being paid to her sister Muffin, the bride. When video is taken of the wedding gifts, Buffy, not wanting to be upstaged, disrobes in front of the nude portrait of Muffin. Dino confides in Wilson about Buffy's pregnancy, and Wilson tells Tracy, who vindictively spreads the rumor. Snooks angrily confronts Dino, who admits sleeping with Buffy but says she also slept with just about every member of his military school barracks, a fact Buffy confirms. Snooks' oft-married sister Marge Spar from New Jersey starts a new romance with the Corellis' gardener, while bridesmaid Rosie Bean is unaware shy friend Shelby Munker is having an affair with Rosie's husband Russell.
Muffin and Dino prepare to leave for their honeymoon in a new car, the Corellis' wedding gift. The naive Muffin is rattled when Rita makes an unexpected pass at her. She then finds Dino in the shower with his groomsman, Reedley Roots, seemingly engaged in a gay sexual encounter. The newlyweds' car is seen driving away and the families assume Dino and Muffin left without saying goodbye. Snooks drives his family back to their hotel. They see Dino's car in a wreck, totaled and in flames, and rush back to the Corelli mansion to share the awful news. The families are grieving when Muffin and Dino appear from upstairs, having never left due to Dino's passing out drunk. It turns out Tracy and Wilson, out for revenge, swiped the newlyweds' car and died in the crash. Tulip decides that this incident was God punishing her for sinful thoughts of having an affair with Mack.
Luigi pays his respects to the dead Nettie. He tells her corpse he has kept his bargain as an obedient servant for 22 years, and no one there knows who he really is, but now he will take his leave. He finds his brother in the bushes, making love with Buffy. Luigi and his brother happily drive away as a half-dressed Buffy waves goodbye.
Several actors who later had notable film or television careers appeared as uncredited extras, including John Malkovich (in one of his first film appearances), Gary Sinise, Laurie Metcalf and George Wendt.
The film was inspired by a remark Altman made while doing publicity for his previous film, 3 Women. Upon being asked what his next movie would be, Altman jokingly replied that he was going to shoot a wedding next. Later, Altman and his production assistant decided to follow through on the idea and began planning the film.
The role of "Bishop Martin" was the final film appearance by longtime actor and director John Cromwell, who died Sept. 26, 1979 at age 91. Cromwell's wife of 33 years, Ruth Nelson, appeared as "Aunt Beatrice Sloan Cory."
A Wedding was the 100th film in which Lillian Gish appeared.
Roger Ebert gave A Wedding three-and-a-half out of four stars, writing: "It begins in comedy, it moves into realms of social observation, it descends into personal revelations that are sometimes tragic, sometimes comic, and then it ends in a way that turns everything back upon itself. The more you think about what Altman's done, the more impressive his accomplishment becomes." Rotten Tomatoes reports a 78% approval rating among critics, based on nine reviews.
Carol Burnett won the Best Actress Award at the San Sebastian International Film Festival [Spain's equivalent of France's Cannes Film Festival].
Carol Burnett won the People's Choice Award for Favorite All-Around Female Entertainer [Film and Television].
Carol Burnett was nominated for a Golden Globe Award for Best Supporting Actress in a Motion Picture.
A Wedding is a comic opera based on Robert Altman's 1978 film A Wedding and was composed by William Bolcom with a libretto written by Robert Altman and Arnold Weinstein.