On Christmas Eve 1945, in Bedford Falls, New York, 38-year-old George Bailey contemplates suicide. The prayers of his family and friends reach heaven, where Angel 2nd class Clarence Odbody is assigned to save George, to earn his wings. Clarence views flashbacks of George’s life: In 1919, 12-year-old George saves his brother Harry from drowning, losing the hearing in his left ear. George prevents the druggist, Mr. Gower, from accidentally poisoning a prescription.
In 1928, George plans to tour the world before college, and is reintroduced to Mary Hatch, who has long had a crush on him. When his father suffers a stroke and dies, George postpones his travel to sort out the family business, Bailey Brothers’ Building and Loan, which boardmember Henry F. Potter wishes to dissolve, but the board votes to keep it open, provided that George runs it. Giving his college tuition to Harry on the condition that Harry take over the Building and Loan when he graduates, George works alongside his uncle Billy.
In 1932, a married Harry returns from college, ready to honor his commitment, but George will not let him turn down an excellent job offer from his father-in-law. George marries Mary. They witness a run on the bank and use their $2,000 honeymoon savings to keep the Building and Loan solvent.
George establishes Bailey Park, a housing development financed by the Building and Loan, in contrast to Potter’s overpriced slums. Potter offers George $20,000 a year to become his assistant, but George realizes Potter intends to shut down the Building and Loan and rebukes him.
During World War II, George is ineligible for service because of his deaf ear. Harry becomes a Navy pilot and earns the Medal of Honor by shooting down a kamikaze plane headed for a troop transport. On Christmas Eve 1945, as the town prepares a hero’s welcome for Harry, Billy goes to deposit $8,000 of the Building and Loan’s cash. At the bank, Billy taunts Potter with a newspaper headline about Harry, but unintentionally wraps the envelope of cash in Potter’s newspaper. Billy discovers he has misplaced the cash, and Potter finds the envelope but says nothing. When a bank examiner reviews the Building and Loan’s records, George realizes scandal and criminal charges will follow. Fruitlessly retracing Billy’s steps, George berates him, and takes out his frustration on his family.
George appeals to Potter for a loan, offering his life insurance policy with $500 in equity as collateral. Based on the policy’s $15,000 nominal value, Potter says George is worth more dead than alive, and phones the police to arrest him for misappropriation of funds. After getting drunk at a bar and praying for help, a suicidal George goes to a nearby bridge. Before George can jump, Clarence dives into the river and is rescued by George.
When George wishes he had never been born, Clarence shows him a timeline in which he never existed. Bedford Falls is named Pottersville, a seedy town occupied by strip clubs, swing halls, and cocktail lounges. Mr. Gower was imprisoned for manslaughter after putting poison in the pills, and George and Mary’s house is derelict. George’s mother reveals that Billy was institutionalized after the Building and Loan failed. In the cemetery where Bailey Park was, George discovers Harry’s grave. The soldiers on the transport ship died because Harry did not save them, since George did not save Harry. George finds Mary, now a spinster who works at the library. When he claims to be her husband, she screams for the police and George flees.
Convinced that Clarence is his guardian angel, George runs to the bridge and begs for his life back. The original reality is restored, and a grateful George rushes home to await his arrest. Mary and Billy arrive, having rallied the townspeople, who donate more than enough to cover the $8,000; the sheriff rips up George’s arrest warrant, and Harry toasts George as “the richest man in town”. George then receives a copy of The Adventures of Tom Sawyer as a gift from Clarence with a note in it reminding George that no man is a failure who has friends, and thanking him for the wings. At that moment, a bell on the Christmas tree rings, which George’s youngest daughter says means an angel has earned his wings. George, his family and friends sing “Auld Lang Syne”.