In 1954 Muir founded an amateur dramatic society, Thorpe Players, in the village of Thorpe, Surrey where he lived for many years. He was a writer and presenter on many shows, including the 1960s satire programmes "That Was The Week That Was" and "The Frost Report". He was well known to television audiences as a team captain on the long-running BBC2 series "Call My Bluff". Muir found unexpected household fame when he undertook voice-overs for advertisements, including Cadbury Dairy Milk Fruit & Nut chocolate "("Everyone's a Fruit and Nut case"", to the tune of the "Danse des mirlitons" from Tchaikovsky's "The Nutcracker"). Other popular advertising campaigns of the period in which Muir appeared included Batchelors' Savoury Rice "("Every grain will drive them insane!")", a coffee advert in which he used the phrase ""impending doom"", and Unigate milk "Humphreys". In the 1960s Muir was Assistant Head of Light Entertainment at the BBC and in 1969 joined London Weekend Television as Head of Entertainment.