Born April 6, 1990 in West Chester, PA, he developed a passion for filmmaking at an early age, and frequently submitted short features in place of a traditional book report or history project. This early exposure to movie cameras eventually awakened an interest in acting that was launched in earnest in 2003 with a small role in M. Night Shyamalan's "The Village." McDermott had initially attended the open casting call with the hope that he could become an extra and observe the director at work, but his audition so impressed Shyamalan that he was cast as a young boy who announces to William Hurt that mysterious creatures that lurk in a nearby forest have arrived in the village. Buoyed by the encouragement from Shyamalan and members of the cast, McDermott began auditioning for other projects.
By 2004, McDermott's resume had expanded to include several television commercials and a recurring role in the PBS series "Windy Acres" (2004). He returned to feature work the following year as the second lead in the independent adventure-drama "Disappearances," with Kris Kristofferson as a Vermont bootlegger who enlists his son (McDermott) into his business. In 2006, McDermott relocated to Los Angeles, where his career truly kicked into overdrive.
The year 2007 saw him add two more independent features to his credits - the midlife crisis comedy "All Along" and David Wain's all-star portmanteau comedy "The Ten." However, 2008 proved to be his breakout year - not only did McDermott land roles on major TV hits like "The Office" (NBC, 2005- ) and "The Medium" (NBC, 2005- ), but he gained considerable acclaim for his performance in "Frozen River." As T.J., the son of a single mother (Melissa Leo) who is forced to smuggle illegal aliens across the Canadian border into America, he showed an impressive range that encompassed everything from teenage angst to a woeful acceptance of his circumstances. McDermott was singled out by numerous critics for the quality of his work, most notably Roger Ebert, who listed him among the top teenage performances of the year. And he found himself among impressive company when he netted an Independent Spirit Award nomination for Best Supporting Actor alongside James Franco for "Milk" (2008), among others.
McDermott also scored a modest hit that year with "Sex Drive" (2008), a raunchy but likable teen comedy in which he played one half of a pair of randy teen boys on the make for any girl who crossed their paths. He finished out the year by filming "Captain Cook's Extraordinary Atlas" (ABC, 2009- ), the pilot for a fantasy-adventure series for director Thomas Schlamme of "The West Wing" (NBC, 1999-2005) fame.