Educated at Eton and Brasenose College, Oxford, Brabourne succeeded to his title when his brother, Norton, was killed in action in 1943. John was only 19 at the time, serving as an officer in the Coldstream Guards in France. His contact with the Mountbatten family began when he was appointed ADC to Lord Louis Mountbatten, then supreme allied commander in south-east Asia. He married Patricia in 1946.
On demobilisation, he first joined a firm making nautical instruments, but - like his parents-in-law, who had famously honeymooned in Hollywood - Brabourne was fascinated by the cinema, and resolved to work in films.
He started as a production manager for Herbert Wilcox, then, in the 1950s, worked with Danny Angel, the tireless producer of such postwar films as The Sea Shall Not Have Them (1955) and Reach for the Sky (1956). Brabourne's first production of his own, Sink the Bismarck! (1959), was in the same mould, followed, two years later, by a period mutiny yarn, HMS Defiant.
Then came an abrupt change of direction. Brabourne joined a consortium set up to introduce Pay-TV, a cable service whose subscribers would buy movies, opera and the arts on a meter. With this service, and cinema distribution in mind, he made film versions of Laurence Olivier's National Theatre productions of Othello (1965) and Strindberg's The Dance of Death (1968), as well as The Mikado (1966). But the Pay-TV idea was too far ahead of its time, and never spread beyond a pilot experiment.
It did, however, leave Brabourne with a taste for classics of one sort or another. In partnership with Richard Goodwin, he produced Franco Zeffirelli's Romeo and Juliet (1968) and, in 1971, Tales of Beatrix Potter. In 1974, they had a runaway success with Murder on the Orient Express.
Meanwhile, television had involved Brabourne in another capacity. The documentary producer Peter Morley had a biographical series in mind on Mountbatten. When Mountbatten demurred, Morley appealed to Brabourne, who persuaded his father-in-law to agree - on condition that Brabourne himself would be associate producer.
Morley offered the project to the BBC. When the corporation mysteriously failed to reply, Brabourne took it to the London ITV company Rediffusion, which eagerly accepted. By the time the 13-part series was completed, however, Rediffusion had lost its contract to Thames Television, and Brabourne had now to help Morley persuade a reluctant Thames to transmit The Life and Times of Lord Mountbatten. Brabourne joined the board of Thames in 1975.
Brabourne and Morley were also involved in efforts to form a British equivalent of the US Academy of Motion Picture Arts and Sciences - along with its celebrated Oscars. Two existing organisations, the British Film Academy and the Society of Film and Television Arts, had agreed to merge, but even together could muster nothing like the resources needed to acquire and convert suitable premises.
At the same time, Richard Cawston was making his BBC-ITV documentary, The Royal Family. The Queen was to be paid a substantial fee for taking part, which, by custom, would be passed to charity. Morley and Brabourne lobbied Mountbatten, who lobbied Prince Philip, who lobbied the Queen. The money went to the new body, Bafta, of which Morley and Brabourne became trustees.
Brabourne was active in many other professional or charitable causes, among them Harold Wilson's working party on the British film industry in 1975. As a producer, he enjoyed other successes, including Up the Junction (1967), Death on the Nile (1978) and his last film, Little Dorrit (1987).
In 1979, Brabourne and his family were aboard Mountbatten's motor yacht when it was blown up by the IRA at Mullaghmore Bay, County Sligo, and Mountbatten was killed. Brabourne and his wife both suffered serious injuries, and one of their sons, 14-year-old Nicholas, died, as did Brabourne's mother, the Dowager Lady Brabourne.
Brabourne seems to have been universally liked, once the handicap of his title, as he saw it, was overcome. He was president of the Kent Trust for Nature Conservation (1958-97), of Wye College (1955-99) and pro-chancellor of the University of Kent (1992-98). He is survived by Patricia, two daughters and four sons.
· John Ulick Knatchbull, 7th Baron Brabourne, film and television producer, born November 9 1924; died September 22 2005