In 1991, 10-year-old Fishel was discovered in a community theater where she performed in two productions, "The Wizard of Oz" and "Peter Pan." She quickly moved on to do voice-overs and commercials, including several as a Barbie Girl for Mattel. Soon after, she appeared on two episodes of the hit show Full House, guest starring as a character named Jennifer. She also had a small role on Harry and the Hendersons, playing Jessica. Fishel's mother eventually became her full-time manager.

In 1993, at the age of 12, she began her well-known role as Topanga Lawrence on ABC's pilot series Boy Meets World. Originally written as a small part, Topanga soon became a recurring role. After a successful first year, Fishel became a show regular. Fishel's character, Topanga, was a spunky, intelligent girl who was mature beyond her years. Throughout the series, a central plot was the relationship between her and main character, Cory Matthews. Their high-school sweetheart romance took them throu