He was born in London and educated at Eton College and Millfield School, Somerset. He then served in the King's Royal Rifle Corps as a 2nd Lieutenant, before going to study at the Byam Shaw School of the Arts, London.

From a distinguished acting dynasty which includes his great-grandfather Herbert Standing (1846-1923) and his grandfather Sir Guy Standing (1873-1937) and his mother, the actress Kay Hammond.

Standing has worked productively on both the London and New York stage, with leading parts in Oscar Wilde's The Importance of Being Earnest, Ring Around the Moon, A Sense of Detachment by John Osborne, and Noel Coward's Private Lives, with Maggie Smith. He made his film debut in The Wild and the Willing (1962), going on to appear in King Rat (1965), The Psychopath (1966), The Eagle Has Landed (1976), The Elephant Man (1980), Nightflyers (1987), Mrs. Dalloway (1997), and A Good Woman (2004).

One of his first major television role was as Sidney Godolphin in the BBC blockbuster, The First Churchills (1969). Other television appearances have included Tinker, Tailor, Soldier, Spy (1979), and The Choir (1995), and King Solomon's Mines (2004). During the 1980s he played opposite Lorraine Chase in the ITV sitcom, The Other 'Arf. In the U.S., he has graced numerous weekly programmes including L.A. Law, Civil Wars and Murder She Wrote, and co-starred briefly with Robert Wagner and the late Samantha Smith in the action series Lime Street (1985).

Standing also appears on the tracks "Elements" and "Ramblin' Man" on electronica duo Lemon Jelly's album Lost Horizons.

He succeeded his father Sir Ronald Leon, as the 4th baronet in 1964. He does not use the title. The Leon family were, until 1937, owners of Bletchley Park, the country house in Buckinghamshire famous as the World War II Enigma code-breaking centre. He married Jill Melford in 1961, but they divorced in 1972. They have a son. In 1984 he married Sarah Kate Forbes, the daughter of film director Bryan Forbes and actress Nanette Newman. They have three children.