During her youth, Gish accumulated significant acting experience that culminated with a starring role in the 1986 teen film Desert Bloom. In 1989, Gish got her first major TV film role in When He's Not a Stranger as a rape victim Lyn McKenna. Gish portrayed Anne Hampton, the doomed second wife of Rhett Butler in 1994 in the TV mini series Scarlett.

In 2001, Gish joined the cast of The X-Files as Special Agent Monica Reyes after series star David Duchovny announced his intention to leave the show. During the eighth and ninth seasons, Gish and fellow newcomer Robert Patrick became the show's principal characters. In 2003, Gish guest-starred on The West Wing playing Elizabeth Bartlet Westin, eldest daughter of President Josiah Bartlet (Martin Sheen).

In 2006, Gish played the role of Julia in the independent movie The Celestine Prophecy and costarred in Candles on Bay Street alongside Eion Bailey and Alicia Silverstone. In the same year, Gish began a continuing major role in the eleven-episode Showtime drama Brotherhood. There she plays fictional Rhode Island State Representative Tommy Caffee's wife Eileen, who strives to maintain a model political family while struggling with adultery and drug abuse.

(wikipedia.org)