The film commences with the grand finale of Halloween Town's Halloween celebrations, which are hailed by Jack as being "the most horrible yet". However, when Jack sneaks away from the adoring citizens, it is revealed that he is tired of the same old Halloween and he wanders off into the woods with his ghost dog, Zero.
While walking through the Hinterlands, Jack stumbles upon a place in the forest he's never been before, discovering a grove of trees that have doors leading to different holiday towns. Jack is drawn towards the Christmas tree-shaped door and opens it, therefore ending up in Christmas Town. Soon after, he becomes infatuated with the holiday. After obsessively researching it, he decides that this year, the citizens of Halloween Town will manage Christmas in the hopes of "improving" it. Sally, an animated rag doll who is secretly in love with Jack, has a premonition that his plans for Christmas will be a disaster and attempts to warn him, but he politely dismisses her fear. Sally's premonition later proves to be right.
Not really understanding the "spirit" of Christmas, the citizens of Halloween Town create a celebration of the macabre rather than a "season to be jolly"; Jack, dressed as Santa Claus, unintentionally brings fear rather than joy to the children of the world. Wanting Santa Claus to rest, Jack had ordered local trick-or-treaters Lock, Shock and Barrel to bring Santa to Halloween Town; however, after Santa was firstly brought to Jack and greeted by him, the three kids took him to Oogie Boogie who teased and eventually planned to kill Santa. Sally attempts to rescue Santa Claus after discovering that military forces are planning to destroy Jack, but she too is captured.
Upon realising the error of his ways, Jack overcomes his identity crisis and reaffirms himself as the Pumpkin King. With determination to set things right, Jack promptly returns to Halloween Town, where he discovers that Santa has been taken to Oogie's Lair. He manages to defeat Oogie and rescue Santa and Sally. Santa returns to the real world to save Christmas and, as a sign of no hard feelings, gives Halloween Town a taste of true Christmas spirit, fulfilling his former desire to a limited extent. Jack finds Sally atop Halloween Hill, which is blanketed in snow, and reveals his own affections for her as the film ends.
The official film soundtrack CD contains an epilogue not in the film, stating that "many years later", Santa returned to Halloween Town to visit Jack, where he discovered that Jack had "four or five skeleton children at hand" who play together in a xylophone band. Given the ending of the movie, it can be assumed that the children are Jack and Sally's offspring.
He debuts in "MCF: A Musical Nightmare" as one of the allies that the MCF team up with to stop Mafiafas and Damien.
- Despite him and Sally being monsters, they adopt Wing, a half human half panther being as their daughter.
- His head made a cameo in "Beetlejuice" and "Vincent".
- Jack is the adopted father of a member of MCF (Wing), a member of RMCF (Homura), and a member of Kid Crusaders (Dawn), making him the only father to have a child in three MCF related groups.
- MCF: A Musical Nightmare(Debut)