Knudsen was born on March 25, 1988, in Toronto, Ontario.[1] His first film debut was in the 2000 film, Tribulation.[2]
In 2001, Knudsen guest starred on The Guardian and appeared in three other episodes. He was nominated for a Young Artist Award for his performance. In 2003, Knudsen starred in the TV series Mental Block. He co-starred as Leroy "Lefty" in the film adaptation of Youth in Revolt,
and in Scott Pilgrim vs. the World as Lucas "Crash" Wilson, who was the lead singer of fictional band Crash and the Boys. In 2005, he co-starred in the horror film Saw II.[3] From 2006 to 2008, he played the series regular role, Dale Turner in the CBS series Jericho.[2]
He portrayed teen tech genius Alec Sadler in the Canadian science fiction series Continuum, starring alongside Rachel Nichols and Victor Webster,[6] and was nominated for Best Supporting Actor for the role for two consecutive years at the Saturn Awards.[7][8] He appears in Bon Cop, Bad Cop 2,[9] the horror feature Darker Than Night,[10] as well as Stephen King-based sci-fi TV series The Mist and space adventure drama series Killjoys.[2]