Coming from a theatrical family, Jack Douglas' entry into show business was as a producer, however, not as a performer. His father was a theatrical producer, and Jack followed in his footsteps at an early age - he produced his first show at 15. Douglas showed no interest in the performing end of the business until one night when one of his actors took ill and, there being no replacement, Douglas put on the character's costume and did it himself. He enjoyed it so much that he soon gave up producing comedies and began performing in them. It wasn't long before he became one of the more recognizable character actors in films, especially in the "Carry On" series, where he played a variation on his most famous character, a nervous, terrified and perpetually fidgety little man.

Enjoyed cooking as a hobby.Great lover of jazz.The only star of the "Carry On..." films who, after starting in the series, appeared in every film subsequently. His first "Carry On..." was Carry on Matron (1972) and his last Carry on Emmannuelle (1978). He also appeared in the one-off Carry on Columbus (1992), but often criticized the film when speaking about it in conversation.His brother Bill Roberton was a theatre director who directed him in the "Carry On London" stage show which ran at London's Victoria Palace from October 1973 to March 1975.