Susan was born to Robert Smith and Gail Dey. She began modeling as a teen and moved to acting, starring as Laurie Partridgeon in The Partridge Family from 1970–1974 at the age of 17. She graduated from Fox Lane High School in Bedford, New York.
Susan married her first husband, Lenny Hirshan in 1976 and divorced in 1981, they had one daughter Sarah Hirshan born 1978. In 1998, she married television producer Bernard Sofronski.