At about the same time Lambert was deeply involved in Britain's Free Cinema movement which called for more social realism in contemporary movies.
In 1954, while still living in England, he wrote his first screenplay, Another Sky, about the sexual awakening of a prim English woman in North Africa.
The Roman Spring of Mrs. Stone (1961) adapted a novella by Tennessee Williams on the affairs of an older actress with a young Italian gigolo.
As, from the 1920s through the late 1960s, homosexuality was rarely portrayed on the screen, gay screenwriters like Lambert learned to express their personal sensibilities discreetly between the lines of a film.
However, in the film version, he was not fully identified as gay because, at Redford's request, the husband he played was changed from homosexual to appear as though he might be bisexual.
Another of Lambert's screenplays was I Never Promised You a Rose Garden (1977), based on a novel by Hannah Green, which describes in layman's terms a teenager's battle with schizophrenia.
According to screenwriter and writer Joseph McBride, he was "a keenly observant, wryly witty chronicler of Hollywood's social mores and artistic achievements."
Working as a Hollywood screenwriter, Lambert was able to interview and gain personal remembrances of most of the cast and crew involved with the film, including dismissed director George Cukor and star Vivien Leigh (Scarlett O'Hara).
In his book, Lambert controversially claimed that Wood frequently dated gay and bisexual men, including director Nicholas Ray and actors Nick Adams, Raymond Burr, James Dean, Tab Hunter, and Scott Marlowe.
Lambert's final book was The Ivan Moffat File: Life Among the Beautiful and Damned in London, Paris, New York and Hollywood (2004).