While on vacation in New York City at the age of 16, she found herself auditioning for a film;[5] although she was not selected, she signed with the William Morris Agency and began her professional acting career.

She went on to make guest appearances on a few other TV shows before landing the recurring role of Ensign Ro Laren in Star Trek: The Next Generation.

She received praise, as well as a Saturn Award nomination from the Academy of Science Fiction, Fantasy & Horror Films, for her performance as photographer Carrie Laughlin in the 1993 thriller Kalifornia.

This was followed with the lead female role in the 1994 black comedy Swimming with Sharks as well as supporting roles in films such as The Road Killers, Just Looking and John Carpenter's 1996 science fiction/action sequel Escape from L.A. She continued performing on television during this period, with guest spots on Seinfeld, The Outer Limits and Star Trek: The Next Generation, to which she returned to tie up the Ro Laren storyline in the series' penultimate episode.

In 1995, she played one of the leads in J. S. Cardone's crime thriller Black Day Blue Night, alongside Mia Sara and Gil Bellows.

"[11] In 1996, Forbes joined the cast of NBC's popular police drama Homicide: Life on the Street, playing chief medical examiner Julianna Cox.

Forbes starred as the lead in the adaptation of the comic-book Global Frequency, the single produced episode of which leaked online the following year, eight months after the series failed to be picked up by Warner Bros.

[12] Forbes returned to British television screens with guest roles in both Holby City and as a Mossad agent in Waking the Dead.

In 2008, Forbes starred in two HBO drama series; In Treatment, portraying the wife of the central character, and in True Blood as a Maenad named Maryann Forrester.