He is known for portraying Daniel Matthews in Saw II, Robbie Mercer in Scream 4, Alec Sadler in Continuum and Dale Turner in the CBS series Jericho.

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.

[4] Knudsen played Ryan in The Barrens, co-starring True Blood's Stephen Moyer, which was released in late 2012.

[5] 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.