[2] Marshall decided to become an actress in the seventh grade after winning a citywide monologue competition in Huntsville, Alabama.
[2] Playing the comedic role of the maid in her middle school's production of Junior Miss led her to focus on character acting.
[2] During the 1980s, Marshall performed in nine Studio Theatre productions, including a 1983 role as Jo, a pregnant waif in Shelagh Delaney's A Taste of Honey, termed Marshall's "breakthrough performance" by friend and Studio Theatre Artistic Director Joy Zinoman.
[2][3] She also drew attention for her roles in Studio Theatre's Miss Margarida's Way and My Sister is in This House, for which she received her first Helen Hayes nomination.
[1][2] Other productions in which she performed during that time included Briar Patch at Arena Stage; The Stick Wife at Horizons; The Vampires at Woolly Mammoth Theatre Company; and Baby with the Bathwater at Round House Theatre in 1989, for which she won the Helen Hayes Award for Outstanding Supporting Actress in a Resident Production.