Marshall was born in Rockville, Maryland and graduated from Robert E. Peary High School in Rockville, in 1982, where she had pursued her love of photography. On October 12, 2003, Marshall married actor Danny Nucci; she gave birth to her first (Nucci's second) child in March 2005.

It was not until 1992 that Marshall gained audience attention when she had a three episode guest role on The Wonder Years and guest-starred on other shows such as Seinfeld (playing the student who reported that Jerry and George were a gay couple), Nash Bridges, Grapevine and Diagnosis Murder. In 1994, she got her first sitcom role on Wild Oats, which was cancelled in its first season. After a few years in B-movies, Marshall gained a role on a second series, 1997's Chicago Sons, which fared no better than Wild Oats. However, in the same year she landed a recurring role on Spin City and starred alongside Bette Midler and Dennis Farina in the film That Old Feeling.

Marshall has gradually developed a reputation for many television series in which she is a main cast member being cancelled in their first season, in addition to several other shows on which she has guest starred being cancelled not long after her appearance. She has also been cast in several pilots that were not picked up, including the Elizabeth Lackey series Cooking Lessons and Rob Thomas's Sticks. As a result, she has been described as a "showkiller" on Television Without Pity.

Marshall's third television series, Rob Thomas's Cupid, premiered in 1998. It featured her as Dr Claire Allen, a psychiatrist supervising a man named Trevor (Jeremy Piven) who thinks he is Cupid. The series gained a small fan base but found itself in a bad time slot and was cancelled. Marshall then joined her That Old Feeling co-star (and later husband) Danny Nucci and Gina Gershon on David E. Kelley's Snoops, about an unconventional detective agency. Snoops was also cancelled in its first season.

In 2000, Marshall returned to television screens: first with a three-episode guest appearance as a porn star and love interest for Jeremy (Joshua Malina) on Aaron Sorkin's Sports Night, and then in her fifth TV series, Cursed (a.k.a The Weber Show). After its first season, Cursed was also cancelled, and Marshall remained off camera until 2002, when she guest starred on Just Shoot Me! as the daughter of Nina Van Horn. Before the year was out, Just Shoot Me! had been cancelled and Marshall was on her sixth series: Hidden Hills. Hidden Hills was an offbeat comedy about three families in suburbia, which was not renewed for a second season despite modest success. Marshall resurfaced in a secondary role in the Steve Martin-Bonnie Hunt remake of Cheaper by the Dozen and had a cameo appearance in Break a Leg, which starred Danny Nucci (Marshall and Nucci were now in a relationship).

In 2004, Marshall guest starred in an episode of Alicia Silverstone's Miss Match, but the series was cancelled before her episode aired. In October, she had a three-episode role in the new series Veronica Mars (created by Cupid's Rob Thomas), which she reprised toward the end of season two. The show was cancelled in May 2007 at the end of its third season. Marshall's next main role was in the sitcom Out of Practice, which was cancelled during its first season.