Sumpter’s first movie role was in the 2001 film Frailty as the young Adam Mieks seen in flashbacks. Sumpter received a Saturn Award nomination for “Best Performance by a Younger Actor” for his performance. Following that, he appeared with Danny Glover in the Showtime film Just a Dream, for which he received a Young Artist Award for “Best Performance in a TV Movie, Mini-Series or Special – Leading Young Actor”. His next film was Local Boys, a family surfing drama, with Mark Harmon and Eric Christian Olsen.

In July 2002, at age 13, Sumpter was selected for the role of Peter Pan. Sumpter did nearly all of his stunts for the film himself. To prepare, he says he practiced sword fighting as much as five hours a day, as well as training in gymnastics and lifting weights. He was working with actress Rachel Hurd-Wood and built a strong relationship with her. While filming in Australia, he supplemented his training with cricket and surfing. Sumpter grew several inches while in the film’s production, requiring staging tricks to retain Captain Hook’s height advantage over Peter in face-to-face scenes late in the process. Producer Lucy Fisher also said that, “The window he flies out of had to be enlarged twice.” Sumpter won both a Saturn and Young Artist Award for the film.

Sumpter spent the summer of 2005 in Oregon filming the teen comedy The Sasquatch Gang (a.k.a. The Sasquatch Dumpling Gang), released in November 2006. He had a small role in the film An American Crime, which played on Showtime in 2008 before going to DVD. He appeared in an episode of CSI: Miami as the boyfriend of a girl whose parents are murdered.

In December 2015, Sumpter announced that he and Lauren Pacheco were engaged to be married, but in October 2016 stated that they were no longer engaged.