In 1919-1920, Captain Thomas Fairfax-Ross acted as assistant private secretary to the Minister of Transport. He retired from the regular army in 1928 and became a stockbroker in the firm of Montagu, Loebl, Stanley and Company of London. He married Alice Enyd Felicite née Chinnery in 1924, and the couple had three children: a son, John and two daughters, Anthea and Christine.
From 1937, Fairfax-Ross commanded the 1st Battalion of the London Rifle Brigade and during the Second World War had command of an infantry brigade from 1941 to 1944. After the war, he served as sub-district commander of the City of London Army Cadet Force from 1945 to 1947, and honorary colonel of the London Rifle Brigade from 1947. In 1946, Thomas Fairfax-Ross was appointed by King George VI as one of His Majesty’s Body Guard of the Honourable Corps of Gentlemen-at-Arms. He died on 16 April 1960 aged 63.