By the late 1960s, Marquand had begun a career directing television documentaries for the BBC, where he worked on projects such as the 1972 series Search for the Nile and an edition of One Pair of Eyes (1968), about the novelist Margaret Drabble who had been a friend of his at Cambridge. He collaborated with the celebrated foreign correspondent James Cameron on a long-running series called Cameron Country for BBC television and also with John Pilger on a series of films for ITV. In 1979, Marquand incorporated many of his documentary techniques in his biographical television movie Birth of the Beatles. He directed several films specifically for children including the 1977 Emmy winning Big Henry and the Polka Dot Kid.

In 1987, Marquand died of a stroke aged 49. His last film, Hearts of Fire, starring Bob Dylan, was released posthumously.