Patrick Cassidy was born January 4, 1962 in Los Angeles, California. He is the son of Shirley Jones and Jack Cassidy. His brothers are Ryan and Shaun Cassidy, and his half-brother is David Cassidy. He is married to actress, Melissa Hurley, and is the father of two sons, Cole Patrick and Jack Gordon.
Cassidy grew up in an Irish-American family and decided to enter his high school's drama program after breaking his collarbone while playing as the quarterback for his high school football team. His first starring television role was in 1981 in the cautionary NBC movie Angel Dusted. Cassidy first appeared on Broadway in 1982 when he took over the role of Frederic in Gilbert and Sullivan's The Pirates of Penzance (having played the role in the national tour in 1981). In 1983, he starred in Bay City Blues as a baseball player in the minor leagues. The show was cancelled after just four episodes. In 1986, he played a West Point cadet in Dress Gray (for which he received an Emmy Award nomination) and appeared in the holiday TV movie Christmas Eve with Loretta Young.
Cassidy's next Broadway role was Jeff Barry in the Ellie Greenwich jukebox musical Leader of the Pack. In 1988, he starred in the television series Dirty Dancing, based on the film. Two years later, he starred in Longtime Companion about an actor battling AIDS, which was the first film to tackle the subject. In 1990, he originated the role of The Balladeer in Stephen Sondheim's Assassins at Playwrights Horizons, an off-Broadway theater.
In 1993, Cassidy starred as Bobby opposite Carol Burnett in a Los Angeles production of Sondheim's musical Company. (He later was passed over for a role in another Sondheim musical, Passion). In 1994, he appeared in the film I'll Do Anything and "How the West Was Fun" with Mary-Kate and Ashley Olsen. In 1995, he portrayed John Wilkes Booth in the Los Angeles Repertory staging of Assassins. In 1997, he had a recurring role on TV's Lois & Clark: The New Adventures of Superman, only to have another Superman related recurring role a few years later as the biological father of Lana Lang in Smallville. In 1998, he was Macheath in an L.A. production of The Threepenny Opera (for which he received the Garland Award for Best Actor). In 1999, he played the title character in a national tour of Joseph and the Amazing Technicolor Dreamcoat. In 2000, Cassidy co-starred with Cheryl Ladd in Annie Get Your Gun on Broadway. In 2001 he played Radames in the national tour of the musical Aida (for which he won the 2002 National Broadway Theatre Award for Best Actor in a Touring Musical) and then appeared in the role on Broadway in 2002. In 2004-05 he was back on Broadway in 42nd Street as Julian Marsh (opposite his mother as Dorothy Brock).