In 2011, he was cast in the action thriller film Looper as Cid Harrington, a child with unusual telekinetic abilities, who becomes a warlord called the "Rainmaker".
Rian Johnson said, "Looking back I'm kind of terrified that I hinged the success of the backend of the movie on finding someone like Pierce.
[8] From 2018 to 2020, he has voiced the character of Tim Templeton on the Netflix animated series The Boss Baby: Back in Business.
In 2020, Gagnon voiced the role of Young Fred Jones in the Scooby-Doo film Scoob!.
Holiday Haunt, which was set for release in 2022 on HBO Max,[9] but it was canceled in August 2022.