A versatile actor and singer who, even in his later years, seemed to retain his youthful appearance, Cassidy made his Broadway debut at the age of 17 in the chorus of the 1943 Cole Porter - Ethel Merman hit musical Something For The Boys. More chorus work followed in Sadie Thompson, The Firebrand Of Florence, Around The World, Music In My Heart, and Inside USA, before Cassidy played a more prominent role, along with others on the brink of success such as Tom Ewell and Alice Pearce, in the stylish revue Small Wonder (1948). He was in the short-lived Alive And Kicking in 1950, and two years later took over the part of Seabee Richard West in South Pacific. Also in 1952, Cassidy had his first leading role as the suave Chick Miller in Wish You Were Here, a show that attracted a great deal of publicity owing to the fact that it had a swimming-pool built into the stage. Cassidy introduced the appealing title song, and also sang the underrated ‘Where Did The Night Go?’. He subsequently played opposite Betty Oakes in the offbeat Sandhog (1954), co-starred with Carol Lawrence in a musical adaptation of James Hilton’s novel Lost Horizon called Shangri-La, and appeared in various musical productions in the US regions and Europe, before returning to Broadway in 1963 with the charming She Loves Me. While Barbara Cook and Daniel Massey resolved their complicated relationship, Cassidy, playing the unctuous ‘resident ladies man’ Steven Kodaly, pursued Barbara Baxley with ‘Ilona’ and ‘Grand Knowing You’. His performance was rewarded with the 1964 Tony Award for Supporting/Featured Actor in a musical.

During the remainder of the 60s, Cassidy had another ultra-smooth role as Hollywood leading man Byron Prong in Fade Out-Fade In (1964), was egotistical columnist Max Mencken in the comic strip spoof It’s A Bird, It’s A Plane, It’s Superman (1966), and played Irishman Phineas Flynn in the Civil War musical Maggie Flynn (1968). In the title role of the latter show was Shirley Jones, the former star of films such as Oklahoma!, Carousel and The Music Man, who was Cassidy’s second wife. Cassidy himself also appeared in a number of films, notably as John Barrymore in W.C. Fields And Me and as Damon Runyon in The Private Files Of J. Edgar Hoover. After his Broadway career declined, he worked in regional theatre, both straight and musical, and appeared on television and in nightclubs. He died at the age of 49 in a fire at his Los Angeles apartment. Three of his sons, Patrick Cassidy and Shaun Cassidy (from his marriage to Shirley Jones), along with David Cassidy (from his earlier marriage to Evelyn Ward), are also in showbusiness.