Tim Allen stars as Scott Calvin, an ordinary man who accidentally causes Santa Claus to fall from his roof on Christmas Eve. When he and his young son, Charlie, finish St. Nick’s trip and deliveries, they go to the North Pole where Scott learns that he must become the new Santa and convince those he loves that he is indeed Santa Claus.
On Christmas Eve, divorced dad Scott Calvin and his son discover Santa Clause has fallen off their roof. When Scott takes the reins of the magical sleigh, he finds he is now the new Santa, and must convince a world of disbelievers, including himself.
Eight years have passed since Scott Calvin took on the mantle of Santa Claus, redeemed himself to be good, and solved The Santa Clause Mystery. Now he has become a great Santa at the North Pole, until Head Elf Bernard and Curtis, the Keeper of the ''Handbook of Christmas'' break the news that there is another clause – the "Mrs. Claus", a mystery of who will marry Scott.
Twelve years have passed since Scott Calvin took on the mantle of Santa Claus, redeemed himself to be good, solved The Santa Clause Mysteries and married Carol Newman, who has now become a teacher in the North Pole. On Christmas Eve, she tells a group of young elves a story from her life with Scott while expecting their first child. Scott invites his in-laws, Sylvia and Bud Newman, to the North Pole, along with Scott's former wife, Laura, her husband, Neil, their daughter, Lucy, and Scott's son, Charlie. Meanwhile, he is summoned to a meeting of the Council of Legendary Figures, consisting of Mother Nature, Father Time, the Easter Bunny, Cupid, the Tooth Fairy, and the Sandman, concerning the behavior of Jack Frost, who is jealous that he has no holiday or special occasion in his honor. Because he has been promoting himself during the Christmas season, Mother Nature suggests sanctions against him. When Scott says he is dealing with how to get the in-laws to come without revealing that he is Santa, Jack Frost negotiates a light sentence of community service at the North Pole, helping Scott and the elves put up various Canadian-themed paraphernalia, as Carol's parents believe Scott is a toy-maker in Canada, which Scott agrees.
After nearly three decades of being Santa Claus, Scott Calvin’s magic begins to falter. As he struggles to keep up with the demands of the job, he discovers a new clause that forces him to rethink his role as Santa and as a father.