Rennie's first appearance on screen was in the indie Canadian film Purple Toast, filmed in 1990 and released in 1993. Also in 1993, he began to take small roles in television (Highlander, Forever Knight, and the revamped version of The Outer Limits). Rennie's profile within the Canadian industry was heightened during this period by leading roles in the television films Paris or Somewhere (1994) and For Those Who Hunt the Wounded Down (1996). Due to several disagreements during the production of the latter film, Rennie vowed never to work for the CBC again, though he has remained a staunch supporter of the Canadian industry as a whole. After his first appearance on The X-Files, he was offered the role of Alex Krycek but turned it down because he did not want to commit to a television series at that time. His career gained momentum quickly and larger roles in Canadian films followed (the independent short film Frank's Cock by Mike Hoolboom, and Mina Shum's Double Happiness as Sandra Oh's love interest, for which he was nominated for a Genie Award as best supporting actor). He also had more important roles on television series, as in a two-parter for La Femme Nikita. 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. The Canadian band Billy Talent is named after his Hard Core Logo character. As for his part in Due South, it has been said that his "disaffected intensity and hungover good looks" added an edge to the series. Rennie was then seen in the recurrent roles of the convenience store guru Newbie on Don McKellar's cult television series Twitch City and of detective Bobby Marlowe on the award-winning series Da Vinci's Inquest. His interpretation of sex marathoner Craig Zwiller in Don McKellar's Last Night earned him his first Genie Award (1999). 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). The same year, he impersonated a chilling yet seductive drifter in Suspicious River. 2002–present With the father characters of Falling Angels (2003) and Flower and Garnet (2002), Rennie expanded to playing more mature roles, rather than young, self-destructive rebels.