The McCallister family is preparing to spend Christmas in Paris, gathering at Peter and Kate's home in a Chicago suburb on the night before their departure. Peter and Kate's youngest son, Kevin, is the subject of ridicule by his older siblings. Later, Kevin accidentally ruins the family dinner and their flight tickets to Paris after a scuffle with his older brother Buzz, resulting in him getting sent to the attic of the house as a punishment, where he berates Kate and wishes that his family would disappear. During the night, heavy winds damage the power lines, which causes a power outage and resets the alarm clocks, causing the family to oversleep. In the confusion and rush to get to the airport, Kevin is accidentally left behind.
Kevin wakes to find the house empty and, thinking that his wish has come true, is overjoyed with his newfound freedom. However, he soon becomes frightened by his next door neighbor, Old Man Marley, who is rumored to be a serial killer who murdered his own family, as well as the "Wet Bandits", Harry and Marv, a pair of burglars who have been breaking into other vacant houses in the neighborhood and have targeted the McCallisters' house. Kevin tricks them into thinking that his family is still home, forcing them to put their plans on hold.
Kate realizes mid-flight that Kevin was left behind, and upon arrival in Paris, the family discovers that all flights for the next two days are booked. Peter and the rest of the family stay in his brother's apartment in Paris, while Kate manages to get a flight back to the United States, but only gets as far as Scranton, Pennsylvania. She attempts to book a flight to Chicago, but again, everything is booked. Unable to accept this, Kate is overheard by Gus Polinski, the lead member of a traveling polka band, who offers to let her travel with them to Chicago on their way to Milwaukee in a moving van, which she gratefully accepts.
Meanwhile, Harry and Marv finally realize that Kevin is home alone, and on Christmas Eve, Kevin overhears them discussing plans to break into his house that night. Kevin starts to miss his family and asks the local Santa Claus impersonator if he could bring his family back for Christmas. He goes to church and watches a choir perform, then meets Old Man Marley, who dispels the rumors about him. He points out his granddaughter in the choir, whom he never gets to meet, as he and his son are estranged; Kevin suggests that he should reconcile with his son.
Kevin returns home and rigs the house with booby traps to take on the burglars. Harry and Marv break in, spring the traps, and suffer various injuries. While the duo pursues Kevin around the house, he calls the police and flees, then lures Harry and Marv into a neighboring home which they previously broke into. They ambush him and prepare to get their revenge, but Marley intervenes and knocks them unconscious with his snow shovel. The police arrive and arrest Harry and Marv, having identified all the houses that they broke into due to Marv's destructive characteristic of flooding them.
On Christmas Day, Kevin is disappointed to find that his family is still gone. He then hears Kate enter the house and call for him; they reconcile and are soon joined by Peter, Buzz, Jeff, Megan, and Linnie, who waited in Paris until they could obtain a direct flight to Chicago. Kevin keeps silent about his encounter with Harry and Marv, although Peter finds Harry's knocked-out gold tooth. Kevin then observes Marley reuniting with his son, daughter-in-law, and granddaughter. Marley notices Kevin, and the pair wave to each other.
Macaulay Culkin as Kevin, a rambunctious eight-year-old with a penchant for creating harmful inventions
Joe Pesci as Harry, a short and hot-headed thief who targets the McCallisters' home with Marv
Daniel Stern as Marv, a tall and dim-witted thief who targets the McCallisters' home with Harry
John Heard as Peter, Kevin's father
Roberts Blossom as Marley, Kevin's elderly neighbor
Catherine O'Hara as Kate, Kevin's mother and Peter's wife
Angela Goethals as Linnie, Kevin's older sister
Devin Ratray as Buzz, Kevin's oldest brother who often gets him into trouble
Gerry Bamman as Uncle Frank, Peter's rude older brother
Hillary Wolf as Megan, Kevin's oldest sister
John Candy as Gus Polinski, a polka musician who helps Kate
Larry Hankin as Officer Balzak
Michael C. Maronna as Jeff, Kevin's older brother
Kristin Minter as Heather, Kevin's oldest cousin
Daiana Campeanu as Sondra, Kevin's older cousin
Jedidiah Cohen as Rod, Kevin's older cousin
Kieran Culkin as Fuller, Kevin's youngest cousin
Senta Moses as Tracy, Kevin's older cousin
Anna Slotky as Brook, Kevin's younger cousin
Terrie Snell as Aunt Leslie, Uncle Frank's wife
Jeffrey Wiseman as Mitch Murphy, an eight-year-old neighbor of the McCallisters whom Heather mistakes for Kevin during the headcount
Virginia Smith as Georgette, Kevin's aunt, wife of Uncle Rob, and mother of Heather and Steffan
Matt Doherty as Steffan, Kevin's older cousin
Ralph Foody as Gangster #1 (Johnny), character in the film Angels with Filthy Souls
Michael Guido as Gangster #2 (Snakes), character in the film Angels with Filthy Souls
Ray Toler as Uncle Rob, Kevin's uncle, younger brother of Peter and Uncle Frank, and father of Heather and Steffan
Billie Bird as Woman in Airport, Irene, who sells Kate her ticket to Dallas
Bill Erwin as Man in Airport, Ed, Irene's husband who agrees with Irene's ticket sale
Gerry Becker as Officer #1
Alan Wilder as Scranton Ticket Agent
Hope Davis as French Ticket Agent
Kenneth Hudson Campbell as a Santa Claus impersonator whom Kevin meets