He succeeded his father as the 4th baronet in 1964, but does not use the title. The Leon family were, until 1937, owners of Bletchley Park, the country house in Buckinghamshire used in the Second World War as a code-breaking centre. His half-sister was the actress Anne Leon, who was married to Michael Gough. He married Jill Melford in 1961; the couple had a son, but divorced in 1972.

In 1984, he married Sarah Kate Forbes, the daughter of film director Bryan Forbes and actress Nanette Newman and the sister of television presenter Emma Forbes; they have three children.

He appeared in the horror film Nightflyers (1987) adapted from a short story by George R. R. Martin. In 2002, he had a speaking credit on Lost Horizons, the second studio album from the British electronic duo Lemon Jelly. On track 1, “Elements”, he lists the basic ‘elements’ that make up the world: ash, metal, water, wood, fire and sky. On track 3, “Ramblin’ Man”, Standing reads a long list of various locations around the world, ranging from small Sussex villages to major world capitals.

In July 2010, it was confirmed that he would be appearing as Jon Arryn in the HBO series Game of Thrones, based on Martin’s A Song of Ice and Fire novels.