Cassidy was born in Richmond Hill, New York to William Cassidy, who was of Irish descent, and Charlotte Koehler, who was of German descent. He achieved his greatest success as a musical performer on Broadway, appearing in Wish You Were Here, Shangri-La, Maggie Flynn, Fade Out - Fade In, It's a Bird...It's a Plane...It's Superman, and She Loves Me, for which he won a Tony Award. He also received Emmy Award nominations for his television performances in He & She (1967) and The Andersonville Trial (1970).
On television he became a frequent guest star, appearing in such programs as Bewitched, Get Smart, Columbo, Hawaii Five-O, Match Game and McCloud. Cassidy turned down the role of Ted Baxter in The Mary Tyler Moore Show, appearing instead as a guest star in a very memorable episode as Ted's highly competitive and equally egocentric brother, Hal. He also co-starred in the movie The Eiger Sanction with Clint Eastwood.
Cassidy was married twice. His first wife was actress Evelyn Ward, who is the mother of his son David. After divorcing Evelyn Ward in 1956, he married actress Shirley Jones. They had three sons: Shaun, Patrick, and Ryan Cassidy and divorced in 1974.
Cassidy died in an apartment fire while he slept on the couch, in West Hollywood, California. News reports at the time attributed it to a lit cigarette. In an eerie coincidence, he had starred in an episode of the TV series Night Gallery, called "The Last Laurel", in which he played a villainous character who discovered the secret of astral projection, and bent on revenge against others, accidentally killed himself while sleeping.
His son, David, wrote about his father's bisexuality in his autobiography.
Cassidy was approved for a star on the Hollywood Walk of Fame in 2005 and fundraising efforts are currently under way to fund the dedication ceremony.
- McGlone, Jackie (2007-03-24). Still a daydreamer. The Scotsman. Retrieved on 2007-04-09.
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