The pair appear in the animated sequel, which sees Trolls Poppy (Kendrick) and Branch (Timberlake) discover that they are from one of six different tribes, each devoted to a different form of music.
The musical film also features appearances from Ozzy Osbourne, Gwen Stefani, and James Corden, but speaking on Britain's "The Graham Norton Show" on Friday, February 14, Kendrick confessed the "Mirrors" hitmaker was tough to work with in the studio.
"He was a monster to work with on the music," she said. "He'd be behind the glass saying, 'Do it again, but better!'."
However, she added: "I really had fun and I knew I was in good hands. He's my parachute."
Timberlake went on to explain: "You're given parameters to be creative within. It was my mission to create music that is for everyone, not just the kids."
And the star teased his own future musical output, adding he's "always in the studio so maybe soon."
"I have so much (unreleased music)," he confessed.
"Trolls World Tour" hits theatres from 11 March.