The film was released to positive reviews for McKellar's direction and Oh's acting. It won awards at the Cannes and Toronto International Film Festivals, and three Genie Awards, including Best Actress for Oh.
In Toronto, a group of friends and family prepare for the end of the world, expected at midnight as the result of a calamity that is not explained, but which has been expected for several months. There has been panic and rioting after the imminent catastrophe was announced, but the chaos has since largely died down, with only sporadic murders and robberies. On the last evening, depressed widower Patrick meets with his family, including his sister Jennifer, for a mock Christmas dinner and celebration, though he leaves prematurely to spend his final hours alone in his apartment. He unexpectedly meets Sandra, who is stranded in the city and attempting to reunite with her new husband Duncan, who works at a power company. Duncan spends much of the day calling his customers to reassure them that their heating gas will be kept on until the very end. Sandra and Duncan have a suicide pact. Although intending to die alone, Patrick invites Sandra up to his apartment and attempts to help her find her husband.
Meanwhile, Patrick's best friend Craig embarks on a nearly non-stop sex marathon as he attempts to fulfill every fantasy he has ever had, pursuing interracial sex, sex with his old French teacher Mme. Carlton, and sex with a virgin, among others. With Sandra in need of a car and Craig having a car collection, Patrick and Sandra visit him and ask for one of his vehicles. Craig at first refuses, wanting to die with a complete collection, but Patrick persuades him to give one up. Craig also attempts to have a homosexual affair with Patrick, one of his fantasies, but Patrick indicates he is not interested in having sex with anyone on his last night.
Duncan is randomly murdered by a rioter, and Craig's car Sandra has borrowed is vandalized. Upon realizing she will not reunite with Duncan, Sandra asks Patrick to join her suicide pact. As midnight approaches, they both sit on the roof facing each other, listening to the song "Guantanamera", each holding a loaded pistol to the other's temple. However, as the final seconds approach, both characters are overcome with emotion and simultaneously let their pistols slip away as they slowly embrace in a kiss. The world finally ends.
Director Don McKellar wrote the screenplay after being approached by the French company Haut et Court, which was putting together a project called "2000, Seen By..." consisting of films depicting the approaching millennium seen from the perspectives of 10 different countries. Fearing a story about the millennium would become dated after 2000, McKellar was inspired to make his film about the end of the world, and asked his friends what they would do if they knew the end was coming, basing his screenplay on their responses. His script does not explain why the world is ending because he did not view that as the point of the story. However, McKellar acknowledged that the film's sun shining throughout the night "seems to suggest some major planetary alignment problems". The film marked McKellar's first attempt at directing a feature film.
For the C$2.2 million budget, McKellar secured the Canadian Broadcasting Corporation as the main sponsor, with Haut et Court providing less than half of the budget. Afterwards, more money was raised. Rhombus Media was a major sponsor.
For the part of Duncan, McKellar cast Canadian director David Cronenberg, with McKellar explaining, "He takes his acting seriously," and "Cronenberg typified a certain type of person for me: a soft-spoken, articulate, careful character who may have a wild interior life- the most sane or the most insane character in the film." Initially concerned about directing and acting at the same time, McKellar opted to keep the direction simple, aiming for a "fairly austere and elegant" style. Shortly before shooting began, he learned a Hollywood film called Armageddon was in the works, but opted to go ahead upon hearing the stories were substantially different.
Last Night was filmed on location in and near Toronto between September 15 and October 19, 1997. Shooting primarily took place at the Macdonald Block and apartment buildings near The Annex. Filmmakers used computers to depict a car being overturned. Cinematographer Douglas Koch used bleach bypass for sad visuals.
Following an advance showing for critics in Paris, Last Night premiered at the Cannes Film Festival in May 1998, in the Directors' Fortnight section. It was the first film played in Canada Perspectives at the Toronto International Film Festival. Afterwards, Lions Gate Entertainment obtained distribution rights in the United States.
McKellar testified before the Parliament of Canada that Last Night played in theatres across Canada, before being replaced in many locations by Meet Joe Black. By mid February 1999, Last Night grossed $400,000 in Canadian theatres, a "respectable" sum, though McKellar noted the film performed better in Athens, Greece than in Toronto.
The film received positive reviews, with Rotten Tomatoes measuring an 84% approval rating of 49 reviews. Roger Ebert gave the film three stars, noting fears of Y2K were prominent when he was writing in December 1999, but Last Night's apocalypse "paints a picture more bittersweet than violent." He found "moments of startling poignancy" in the last two-thirds of the film. Stephen Holden of The New York Times called the film "a smart, stiff-upper-lip alternative to a movie like Armageddon," and said McKellar and Sandra Oh give "intense performances," but expected more panic in the case of the apocalypse. Entertainment Weekly gave the film an A-, calling it "a surreal, elegantly melancholy, and yet witty ensemble story" and Oh a "scene-stealer." Peter Howell of the Toronto Star commented on the many Canadian cast members, suggesting the film is "too damn Canuck for its own good," and a riot scene would help. For Maclean's, Tanya Davies declared it "A millennial coup". Outside North America, critics favoured the film as "the perfect antidote" to U.S. apocalyptic films, with a U.K. critic adding "Only in Canada can you get away with a film like this." Time Out called the film "a witty, perceptive movie, exceptionally well structured."
In 2002, readers of Playback magazine voted Last Night the ninth greatest Canadian film of all-time. In 2012, Oliver Lyttelton of IndieWire named it one of five "underseen" apocalypse films worth seeing, writing it compared well to Armageddon and Deep Impact (1998) for "its quiet, character driven approach," and that it was likely the inspiration for Seeking a Friend for the End of the World (2012). In 2014, Colin McNeil of Metro News wrote "Last Night is perhaps the most upbeat end-of-the-world movie you’ll ever see."
McKellar won the "Award of the Youth" at the Cannes Film Festival and Best Canadian First Feature Film at the 1998 Toronto International Film Festival for Last Night. The film also won three Genie Awards, where McKellar was effectively competing against himself as a screenwriter of both Last Night and The Red Violin.