Muir was born on 6 March 1912, the son of Captain (later Colonel) Garnet Wolseley Muir, who became commanding officer of the
Argyll and Sutherland Highlanders in 1923. Muir was educated at
Malvern College and was commissioned 2nd lieutenant in the Argylls in 1932, aged 20. He served on the
North-West Frontier of India from 1935 to 1938, and during the
Second World War saw active service in the Sudan, North Africa, Italy, France, and Germany. At the end of the war, he held the rank of acting lieutenant-colonel and had been
mentioned in dispatches. After service with the
provost marshal's branch of the War Office, in early 1950 Major Muir was posted to the Argylls' 1st Battalion in Hong Kong. In August 1950 the battalion moved to Korea, among the first British troops to join the
United Nations forces in the
Korean War. ==Burial==