In a vibrant and colorful world, the perpetually happy and singing Trolls lead a blissful life, celebrating with parties and spreading joy amongst themselves. The leader of the Trolls, Princess Poppy, embodies the unceasing optimism and energetic spirit of her kind. However, their world is turned upside down when the Troll’s ancient enemies, the gloomy and miserable creatures known as Bergens, invade their village during a raucous celebration. The Bergens believe that the only way to experience happiness is by consuming Trolls, and in a surprise attack, they capture several of Poppy's friends to be the main course at a feast called Trollstice, a Bergen holiday centered around eating Trolls to gain happiness.

Faced with the darkest hour their kind has ever known, the eternally cheerful Poppy refuses to accept defeat. She embarks on a daring rescue mission, determined to save her captured friends from the clutches of the Bergens. On her journey, Poppy enlists the help of Branch, a pessimistic and survivalist Troll who is the polar opposite of Poppy in disposition. Branch has long isolated himself from the other Trolls and prepares for the worst, having lost all hope in the idea of a happy ending. The unlikely pair must work together and venture far beyond the only world they have ever known, confronting challenges and strange new creatures, in a quest that will test their strength and reveal the true power of positivity and friendship.