Dekker began acting at age six, when he received a minor role on "The Young and the Restless" (1973). A year later he was given the opportunity to act with Patrick Stewart, Malcolm McDowell and William Shatner in Star Trek: Generations (1994), playing Thomas Picard. He went on to score guest spots on "The Nanny" (1993), "Seinfeld" (1990), "Star Trek: Voyager" (1995) and "Caroline in the City" (1995) before finally landing a regular spot on Disney Channel's "Honey, I Shrunk the Kids: The TV Show" (1997). For three years he took on the role of Nick Szalinkski, creating a name for himself and finding a nice niche in the Disney universe.
A big break presented itself when he was cast as Zach in the first season of "Heroes". Next up, Dekker was cast as John Connor in Fox's "Terminator: The Sarah Connor Chronicles" (2008) in 2008. Dekker also took on the role of Aidan, a troubled teen in the horror flick From Within (2008). Meanwhile, he also took part in the web-based series "IQ-145" (2008). Though his biggest project came when he decided to try his hand in film production. He wrote, directed and starred in Whore (2008), a film about a group of teenagers who travel to Hollywood to pursue their dreams but discover a much darker side to fame. A year later, he played Taylor Ambrose, a Leukemia patient in the drama My Sister's Keeper (2009) alongside Cameron Diaz and Abigail Breslin. In early 2010, he took a stab as Jesse Braun in the re-imagining of A Nightmare on Elm Street (2010). Dekker's most recent role is Lance Loud in Cinema Verite (2012) with Diane Lane, Tim Robbins and James Gandolfini.