A graduate of Montreal's McGill University, Gilsig headed south to Massachusetts where she excelled in the Harvard University-sponsored Institute of Advanced Theater Training at the American Repertory Theatre (ART). Completing her two-year course in 1995, the actress headed to NYC, but soon returned to Cambridge when the theater bucked policy and hired the actress for their professional theater though she was a new graduate. With ART she starred as Miranda in "The Tempest" (1995) and was featured in Moliere's "Tartuffe" (1996), and evinced a well-rounded spirit of both feminine nurturing and feminist strength in her portrayals. Returning to Manhattan, she was featured on stage in the Primary Stages production "Mere Mortals and Others" (1997) and co-starred in 1998's "Gun-Shy", a presentation at Playwrights Horizons. 1998 also saw her take on a lead voice role in the animated feature "Quest for Camelot", playing a young female hero, a girl who dreams of following in the footsteps of her father and serving as a noble knight of King Arthur's court.

More TV guest work followed for the actress, who had a role in the syndicated series "Viper" in 1998, and was featured on episodes of UPN's "The Sentinel" and "7 Days" the next year. 1999 also saw her begin her alliance with David E Kelley, when she played Assistant District Attorney Jennifer Liner on two memorably disturbing episodes of "The Practice". Her performance led to a part replacing Paula Marshall on "Snoops", but before Gilsig's character could hit screens, the series was cancelled. Keeping the bright hopeful in mind, Kelley began work on "Boston Public" and wrote the idealistic social studies teacher Lauren Davis for the actress. "Boston Public" was a controversial show that kept the industry buzzing, and the actress admirably rose to the challenge of portraying the optimistic but frazzled Ms. Davis, showing both her commitment and frustration, her dedication and her increasingly shaky idealism.