The movie is centered on Fotoula "Toula" Portokalos, a Greek-American woman (Nia Vardalos, who also wrote the script), who falls in love with a non-Greek American, Ian Miller (played by John Corbett). The movie also examines the protagonist's relationship with her family, with their cultural heritage and value system, which is sometimes rocky but ends with mutual appreciation.
Toula is going through an early midlife crisis. At thirty, she is the only woman in her family who has "failed" in Greek terms (her family expects her to marry a Greek, have Greek babies and feed everyone). Because of her failure as a Greek woman, Toula is stuck running the family business, a restaurant, "Dancing Zorba's". In contrast to her "perfect" sister, Athena, Toula is a frumpy, cynical character who can barely articulate her desires and merely wishes for happiness. Now thirty, she fears she's doomed to be stuck with her life as it is.
At the restaurant, she encounters Ian Miller, a school teacher. His presence reminds her of the nearby city college, which she's considered for some time, secretly looking at their catalogs. With mom Maria's help, she talks her father "Gus" (Kostas) into letting her sign up for computer classes, which she says she can use to help improve the business. Now caring more about her appearance, she abandons her unflattering eyeglasses for contact lenses and begins to wear makeup and attractive dresses. A bulletin at the school announces a seminar for computer systems related to travel agencies. Toula's Aunt Voula runs such an agency, and Toula decides to change jobs to work for her aunt. With her aunt and mother, she engages in an intricate scheme to convince her father that it was "his" idea to allow her to work for the travel agency so he will allow Toula to leave the restaurant business.
Toula feels much better in her new job, especially when she notices Ian hanging around looking at her through the window. They finally introduce themselves and go out for dinner. Ian at first does not recognize that she is the once-frumpy waitress from Zorba's, but even when he does, he tells Toula he wishes to spend time with her.
The affair quickly becomes a passionate whirlwind courtship which Toula keeps secret from her family until some weeks later. Toula's cousin Nikki warns Toula that a nosy neighbor saw her kissing Ian and told the family. Gus throws a fit because Ian is "xenos", a foreigner. Ian politely asks permission to continue seeing her, but Gus stubbornly refuses. Toula and Ian still manage to visit his apartment, where their relationship becomes more intimate. Toula meets Ian's upper-middle class, WASP parents for the first time, who are as reserved as her family is demonstrative.
Ian proposes, she accepts, and Gus is ultimately forced to accept their relationship. Ian readily agrees to convert to the Greek Orthodox faith in order to be worthy of Toula, and is baptized in traditional fashion. At the family's Easter festival, Ian confesses he is a vegetarian — a brief crisis for the entire family ensues — and he has a lot of trouble pronouncing Greek words. (He tries to say Khristos Anesti (Christ is risen), and it comes out Cheese straws are nasty.) This becomes a popular running gag with Toula's younger brother Nick. When Ian asks how to say "thank you" to Toula's mom Maria, Nick gives him the words "Oréa viziá," — "Nice boobs!". But Maria slaps Nick, not Ian, knowing full well who taught him.
As the year passes, the wedding planning hits snag after snag as Toula's relatives "helpfully" interfere. Toula is horrified to learn that her parents invited the entire family to a "quiet" dinner, and the Millers, unused to such cultural fervor, are woefully overwhelmed. They brought a Bundt cake, but Maria is bemused by the hole and puts a potted flower in the middle. Meanwhile, Ian wants to invite the guests inside, and warily consults Nick. After confirming the words with cousin Angelo, Ian calls out "έχω τρία αρχίδια" ("I have three testicles"). Gus still doesn't see how the relationship can work out, but others in the family are encouraging; in a touching scene, Yiayia (Gus' mother) shows Toula some of her private treasures, including pictures of herself as a girl and her stefana [wedding crowns], which she gives Toula to wear. Nick secretly comes to Toula to confide that her courage in changing her life has inspired him to do likewise, and he plans to attend the city college to study art.
The wedding day dawns with liveliness and hysteria. Toula is horrified to find she has a stress zit, but covers it with foundation. Maria brings out an elaborate wedding dress, which Toula declares makes her look like a "snow beast". The traditional wedding itself is quiet, dignified, and goes without a hitch. Everyone goes to the reception, and the Millers (fortified with many glasses of ouzo) begin to enjoy the Greek partying lifestyle. Gus gives a speech, in which he analyzes the name "Miller" as having come from the Greek "milo", meaning "apple". He then declares that, since his own last name "Portokalos" means "orange", the two families are "...apples and oranges. We're different but, in the end, we're all fruit". During the final scene where many of the party goers engage in a group dance, Aunt Voula watches Ian dancing with Toula and declares with quiet passion, "...he LOOKS Greek!"
According to Greek tradition, Gus and Maria have bought a gift for the young couple: a house (right next door to them). The film's epilogue shows the Millers' life a few years later; they have a daughter named Paris, who would rather attend Girl Scouts than Greek school, but Toula promises the child that she can marry anyone she chooses.
After a February 2002 premiere, it was initially released in the USA April 19, 2002. That summer it opened in Iceland, Israel, Greece, and Canada. The following fall and winter it opened in Turkey, UK, New Zealand, Argentina, Australia, Hong Kong, Brazil, Norway, the Netherlands, Czech Republic, Spain, Belgium, Italy, Taiwan, the Philippines, Egypt, Peru, Sweden, Mexico, Hungary, Germany, Austria, Switzerland (German speaking region), France, Poland, Kuwait, Estonia, and Lithuania. It was finally released in South Korea in March 2003, and Japan in July 2003.
Martin Grove of Hollywood Reporter wrote, "Tom Hanks and Rita Wilson [...] found 'Wedding' when it was a one-woman Nia Vardalos play in L.A. and believed in it so much that they got it made as a movie".