Star Trek: Deep Space 9 - Paper Dolls - Hellraiser III: Hell on Earth

After 18 months of modeling, she studied acting while still modeling on the side. Her first major roles were in the short-lived 1984 television series Paper Dolls, playing a model, and in the feature film Back to School with Rodney Dangerfield.

In 1989, she began studying acting with Stella Adler and appeared in a number of guest-starring roles in series, including Quantum Leap and The Cosby Show. In 1992, she played Cat in a second pilot for a U.S. version of Red Dwarf, which was not picked up.

Soon after the Red Dwarf USA project folded, she was offered a lead role in Star Trek: Deep Space Nine. Farrell starred as Jadzia Dax, the space station's Starfleet science officer, a character from an alien species known as the Trill, who is host to a 300-year-old symbiont and can draw upon the memories and knowledge of the symbiont's seven previous hosts. The series debuted in January 1993. When she decided to leave the show at the end of the sixth season, Paramount killed off Farrell's "host" character (though continuing the "symbiont" character in a new Dax host, played by Nicole DeBoer).

Farrell then co-starred on Paramount's television comedy series Becker. She played Regina "Reggie" Kostas, foil and love interest to Ted Danson's John Becker, for four years and 94 episodes, before she was replaced by Nancy Travis.

Farrell also provided the voice of Six of One in the animated short film Tripping the Rift, which eventually became a Sci-Fi Channel TV series with other actors providing the voice of Six. First released independently on the Internet, Tripping the Rift originally featured Patricia Beckmann as the voice of Six and was replaced by Farrell's voice for an episode of the Sci-Fi Channel's short film series Exposure, in which Farrell was the guest host. Farrell's version of Six was heard only once on television.

Farrell retired in 2002, after marrying actor Brian Baker. They divorced in 2015 and Farrell played a role in the web-released fan film Star Trek: Renegades. She is expected to appear in the same role in episodes of the fan film web series Renegades, which strips mention of Star Trek for legal purposes.