Before starring in The Partridge Family, Shirley was already a famous singer and actress. She starred in several movies such as Oklahoma, Carousel, The Music Man, and the award-winning Elmer Gantry, co-starring with Burt Lancaster.
She married actor Jack Cassidy and was David Cassidy's stepmother. Shirley and David both starred in The Partridge Family beginning in 1970.
She is a registered Republican who appeared at the 1988 Republican Convention and sang the National Anthem.