Born in Toronto, Ontario, Canada, Douglas Smith is the son of Terrea, an American teacher, and Maurice Smith, a British-born, Vancouver-based producer of low-budget films. He is also the younger brother of Gregory Smith, an actor who previously starred on the TV drama Everwood.
As a teenager, Smith went to Australia to star in a series called Out There where he played the lead role of Reilly Evans. He then landed his first lead horror film in 2003 in Hangman’s Curse where he starred as Elijah Springfield. In the same movie, he worked alongside Gossip Girl star Leighton Meester in a plot where bullying students are becoming deathly ill after screaming the name of a legendary ghost. Subsequently, he landed more TV gigs, including guest roles on Stuck in the Middle with You, Cold Case, Everwood, Joan of Arcadia, The Guardian, CSI: Miami, CSI, Crossing Jordan and Close to Home. After a string of appearances, he became a cast member of HBO’s Big Love as Ben Henrickson, the eldest son of polygamist Bill Henrickson.
Aside from the small screen, Smith also worked on a lot of movies such as the comedy flick Sleepover, the basketball drama Rock the Paint, the fantasy comedy Santa's Slay, and the suspense thriller State’s Evidence.
In 2006, Smith landed the lead role in Citizen Duane, a dramedy about teen-aged Don Quixote born into a family of misfortune. He played the character of Duane Balfour, who decides to sets his sights higher by running for town mayor after losing high school election, and worked alongside Devon Bostick, Vivica A. Fox, Donal Logue, Alberta Watson and Jane McGregor. The following year, he was also given the opportunity to work with Leighton Meester again in the movie The Beautiful Ordinary, a comedy that takes place over 24-hours of teenage wasteland suburbia of 1999.