Forbes was born John Theobald Clarke on 22 July 1926[3][4] in Queen Mary's Hospital,[5] Stratford, West Ham, London.

[10][11] He completed four years of military service in the Intelligence Corps and Combined Forces Entertainment Unit, during which time he started to write short stories.

[10][11] After completing his military service in 1948, following British Equity rules, he was obliged to change his name to avoid confusion with actor John Clark.

[12] Forbes began to act, appearing on stage and playing numerous supporting roles in British films, in particular An Inspector Calls (1954) and The Colditz Story (1955).

[2][3][13] He published a short story collection in the early 1950s, which induced producer "Cubby" Broccoli to offer him screenwriting work on The Black Knight (1954).

[11] He received his first credit for Second World War film The Cockleshell Heroes (1955),[4][11] while other early screenplays include I Was Monty's Double (1958),[2] and The League of Gentlemen (1960), his breakthrough.

The film recounted a bank heist carried out by ex-army officers, and gained critical success, including his first BAFTA nomination.

[13] Beaver Films made The Angry Silence (1960), a controversial Bafta-winning screenplay[14] by Forbes in which Attenborough took the lead role, and the two men shared production responsibilities.

[3][13] Forbes's directorial debut came with Whistle Down the Wind (1961), again produced by Attenborough, a critically acclaimed film about three northern children who conceal a criminal in their barn, believing him to be a reincarnated Jesus Christ.

[3][4] The L-Shaped Room (1962), his next film as director, with Leslie Caron in the female lead, led to her gaining a nomination for an Oscar, and winning the BAFTA (Best British Actress) and Golden Globe awards.

"[18] Coinciding with his time at EMI Films,[20] he resumed directorial work with The Raging Moon (1971), starring his wife, Nanette Newman, and Malcolm McDowell.

(Some of the concert footage was later licensed for the Eagle Vision Classic Albums series Goodbye Yellow Brick Road documentary.)

During filming, Forbes formed a close friendship with John and Taupin, which led to other collaborations with them, including photography on the Don't Shoot Me I'm Only the Piano Player and Goodbye Yellow Brick Road album sleeves.

[13] The thriller about the backlash against the Women's Liberation Movement in the U.S., in which Newman had a supporting role, was to become Forbes's best-known film, partly because of the protests against it.

[13] Forbes was diagnosed with multiple sclerosis in 1975, while working on The Slipper and the Rose; he remained in remission, which he attributed to cutting out gluten and taking vitamins and oil of primrose, together with Newman's care.

Film critic Mark Kermode wrote: "Once had the fan-boyish pleasure of telling Bryan Forbes how much I loved [The] Stepford Wives.