[1] Rennie's television roles include Leoben Conoy / Number 2 on Battlestar Galactica (2003–09), Lew Ashby on Californication (2008–13), Rick Felder on The Killing (2011–12), Gary Connell on The Man in the High Castle (2016), Karl Malus on Jessica Jones (2018), and Commander Rayner on Star Trek: Discovery (2024).

His most prominent early roles were as guitar player Billy Tallent in Bruce McDonald's Hard Core Logo (1996) and as detective Stanley Raymond Kowalski in the third and fourth seasons of CTV series Due South, which aired in over 150 countries.

After a role in David Cronenberg's eXistenZ (1999), his first international success on the big screen was his appearance as the thug Dodd in Christopher Nolan's Memento (2000).

He also impersonated self-controlled Inspector Wood in the period drama Torso: The Evelyn Dick Story (2002) and appeared as the quiet dyslexic painter of Wilby Wonderful (2004).

He has played guest roles in episodes of various Canadian or US television series like Mutant X, The Dead Zone, Smallville, Supernatural, The L Word, Bionic Woman and more recently Harper's Island.

During the same time, he has interpreted contrasting characters in movies such as The Butterfly Effect, H2O: the Last Prime Minister, The Five People You Meet in Heaven, Blade: Trinity (2004), Lucid (2005), Unnatural & Accidental (2006), The Invisible, Tin Man, Normal, Silk (2007), and The X-Files: I Want to Believe (2008).

His recurring role as the Cylon Leoben Conoy in the reimagined Battlestar Galactica (2003–09) and his portrayal of the record producer Lew Ashby throughout the second season of Californication (2008) have earned him a new wide and international recognition.

Trigger is part of several films set in the same universe as Hard Core Logo, directed again by Bruce McDonald; this one, starring Molly Parker and Tracy Wright, written by Daniel MacIvor, is about the reunion of two women who used to be in an alternative rock band together.

Another film, Faith, Fraud & Minimum Wage,[15] based on Canadian playwright Josh MacDonald's play Halo, has been completed and is waiting for release.

Rennie made a number of television appearances in 2011, including a supporting role on The Killing as Rick Felder, Detective Sarah Linden's fiancé.

[18] Rennie likes painting and admires abstract expressionist artists such as Basquiat, Motherwell and Pollock (the Champion spark-plug logo tattoo on his right arm is an homage to Stuart Davis).