Adult acting career
O'Sullivan featured in the 1963 blockbuster film Cleopatra as Pharaoh Ptolemy XIII, the younger brother of the title character played by Elizabeth Taylor.
For the remainder of the 1960s, O'Sullivan was a jobbing actor appearing in such TV series as Dr. Syn, Alias the Scarecrow, Emergency Ward 10, Redcap, Danger Man, No Hiding Place, Dixon of Dock Green, and Strange Report among others, until he was offered the role of Lawrence Bingham in the LWT sitcom Doctor at Large (1971), a role which continued in the later Doctor in Charge (1972–73). Meanwhile, he also had a main role in the Thames Television comedy Alcock and Gander (1972) with Beryl Reid.
By then a regular in TV sitcoms, he starred as Robin Tripp, a trainee chef, in the flatshare sitcom Man About the House written by Johnnie Mortimer and Brian Cooke, launched in 1973. The series was a huge success and was considered risqué due to Tripp sharing a flat with two young women, played by Paula Wilcox and Sally Thomsett, whilst under the watchful eye of their landlords, played by Yootha Joyce and Brian Murphy. A feature film version of the series was released in 1974. In 1975, O'Sullivan starred in the stage comedy Boeing Boeing, undertaking two record-breaking national tours, alongside three of his Man About the House co-stars, Joyce, Thomsett and Doug Fisher.
When Man About the House ended in 1976, O'Sullivan continued playing Robin Tripp in the spin-off sitcom Robin's Nest, in which Robin sets up a bistro with funding from his girlfriend Vicky's father, James Nicholls (Tony Britton).
Robin's Nest was a ratings success, and was the first UK sitcom to feature an unmarried couple cohabiting. To tie in with the series, O'Sullivan wrote a recipe book called Man About the Kitchen, and a sequel Roastin' with Richard, which were published in 1980. He also wrote the Robin's Nest theme tune, which was arranged by Brian Bennett. During that period, O'Sullivan also appeared in adverts for British Gas.
In 1979, O'Sullivan starred in the title role of LWT's drama series Dick Turpin, which ran until 1982. He then played the widower Simon Harrup in the sitcom Me and My Girl, broadcast from 1984 to 1988, co-starring Tim Brooke-Taylor and Joan Sanderson, also produced by LWT. He also appeared in a one-off comedy-drama The Giftie, shown on Channel Four in 1988, in which he and a friend (John Wells) discovered a photocopier at work that could duplicate living copies of themselves, unwisely doing so, and predictably leading to mistaken identities and chaos. In the 1990s, his profile diminished, although he was never short of work. His final acting role was in a 1996 one-off satire titled Holed, with Tony Robinson, about a suburban golf club.
O'Sullivan largely retired from public life in 1996. His last appearance on television was as a guest on a 1999 edition of This Is Your Life held in honour of his Doctor... co-star George Layton. O'Sullivan had himself been the subject of the show in 1974. In 2006, O'Sullivan recorded a commentary for the DVD release of Carry On Teacher.
