Unger made her film debut playing a sympathetic nurse in "Prisoner of the Sun/Blood Oath" (1990) which required a nude scene. She was featured in cinematographer John Seale's directorial debut "Till There Was You" (1991) before moving to the United States. In 1992, Unger earned critical praise for portraying a psychiatric patient with sadomasochistic fantasies in "Whispers in the Dark". She was the brainy Lorraine opposite Tim Roth in the little seen "No Way Home" (1996). "Crash" significantly raised her profile. Rated NC-17 in the USA for its explicit sex, "Crash" met with a mixed critical reception. Unger again appeared nude in several love scenes, notably one with James Spader (as her husband) during which she questions him about the textures and smells of the car's back seat. She was again cast opposite Spader as his drug-abusing wife in the comic melodrama "Keys to Tulsa" (1997) and supported Michael Douglas and Sean Penn in David Fincher's "The Game" (also 1997).

After appearing as the sultry siren Ava Gardner in the made-for-HBO feature, “The Rat Pack” (1998), Unger appeared in the period romance, “Sunshine” (2000), an epic tale about three generations of a wealthy Jewish-Hungarian family ravaged by World War II and post-war Stalinism. Unger was nominated for a Best Supporting Actress Genie award—Canada’s equivalent to the Oscar—for her performance. Meanwhile, Unger helped Gregg Henry pull a double-cross against Mel Gibson after a successful heist in “Payback” (1999), Brian Helgeland's revenge thriller based on the Donald E. Westlake novel, The Hunter. In Norman Jewison’s award-winning biography “The Hurricane” (1999), Unger played Lisa, a Canadian activist who helps get former boxing champ Ruben “Hurricane” Carter released from prison after being sentenced for a murder he did not commit. Unger found her way into a couple of smaller films—“The Weekend” (2000) and “Signs & Wonders” (also 2000)—before appearing in “The Salton Sea” (2002) as the drug-addled neighbor to Danny (Val Kilmer) who is trying to escape savage beatings courtesy of her speed-freak boyfriend (Luis Guzman).

In “Thirteen” (2003), the controversial and oft-lauded teen drama about sex, drugs and thirteen year-old girls, Unger played Brooke, guardian to the beautiful and popular Evie (Nikki Reed) who offers zero boundaries or guidance for her legal daughter. The film was widely recognized for its acting—nominations for Golden Globes and SAG awards were bestowed upon co-stars Evan Rachel Wood and Holly Hunter—but Unger was largely ignored. Appearing as a bookstore owner who has communicated with the dead, Unger added the supernatural thriller “White Noise” (2005) to her extensive resume. Despite a decent take at the box office and Michael Keaton in the lead, “White Noise” failed to impress critics, who felt the film lacked coherency and possessed too much pedagogy. Meanwhile, she had a brief but effective role as the wife of a distraught man (James Remar) in the murder thriller “Fear X” (2005).

Unger next costarred in “Silent Hill” (2006), a supernatural horror feature based on the popular video game about a desperate mother (Radha Mitchell) trying to find an answer to her daughter’s mysterious recurring dream that forces her to sleepwalk. Over the objections of her husband (Sean Bean), she takes her to a fog-shrouded ghost town inhabited by a variety of strange beings—including demons—and overcome by a living darkness that transforms everything it touches. Unger played another desperate mother who lost her own daughter in the strange and evil town. Despite negative reviews, “Silent Hill” opened number one at the box office with over $20 million in box office dollars.