At the age of 12, shortly after she moved with her family to Los Angeles, she was cast as Nicole Bradford in the TV series My Two Dads. The series ran from 1987 to 1990. During the 1990-91 season, she co-starred in the short-lived series Going Places with Alan Ruck, Heather Locklear, and Hallie Todd. The following year, Keanan was cast as Dana Foster in the TV series Step by Step which aired from 1991 to 1998. By 1997 Keanan had changed her name from Staci to Stacy.