Kelly attended St. Mary High School[1] and served in the United States Marine Corps during the Korean War.

Following minor roles in Adventures in Paradise, The Beverly Hillbillies, and The Rifleman, Kelly starred in two television series, NBC's 21 Beacon Street (1959), with Dennis Morgan and Joanna Barnes,[4] and ABC's Straightaway (1961-1962) with John Ashley.

The success of Flipper, which was filmed in Miami and the Bahamas, led to a brief movie career, including a lead in Around the World Under the Sea (1966).

In 1970, Kelly sought to change his image by playing the role of Robin Stone in The Love Machine, based on the novel by Jacqueline Susann.

[5] Kelly—whom Susann had called "the perfect Robin Stone"—won a legal settlement in the case but the accident ended his acting career.