Marlar played first-class cricket for Cambridge University, winning a blue in 1951, 1952 and 1953 (when he captained Cambridge to victory over Oxford), and Sussex between 1951 and 1968. An innovative off-break bowler, he took 970 wickets in 289 matches at an average of 25.22, with a personal best of 9/46 against Lancashire at Hove in 1955. He was a "shrewd and skilful" captain of Sussex between 1955 and 1959. He remains only one of five native-born cricketers to hold this post.
He had a successful journalistic career as an outspoken cricket correspondent of The Sunday Times, and wrote the illustrated history The Story of Cricket (1979).