Bentine was born in Watford, England, of Anglo-Peruvian parentage. In World War II he served as an RAF Intelligence officer, and took part in the liberation of Bergen-Belsen concentration camp. He had acted before the war, and afterwards he decided to become a comedian, specialising in off-the-wall humour, often involving cartoons and other types of animation. For example, a prominent feature of his series, It's a Square World, was the imaginary flea-circus. He was also a television presenter and writer.
He appeared in the Goon Show film Down Among the Zed Men, and at the time seemed perhaps the most comfortable of the cast in working in a visual medium.
In later life, his interests included parapsychology. This partly arose as a result of the premature death of his son.