Born in Rhodesia, Reid-Daly entered military service in 1951 and served with the C (Rhodesia) Squadron of the British Special Air Services (SAS) in operations against insurgents in Malaya. Rising to the rank of Regimental Sergeant Major in the Rhodesian Light Infantry, he was later commissioned and achieved the rank of Captain. He retired from the Army in 1973.
In late 1973 he was persuaded by General Peter Walls, then chief of the Rhodesian Army, to return to active duty in order to form the Selous Scouts, an elite special forces unit to combat the growing threat posed by nationalist guerrillas. Drawing on his Malayan experiences, Lieutenant Colonel Reid-Daly built up a skilled and highly professional regiment from scratch. Although the Selous Scouts achieved many of their military objectives, their unorthodox methods created tensions within the military hierarchy. Reid-Daly had several brushes with the Rhodesian authorities.
In 1979 charges were laid against Reid-Daly for using Scouts for ivory poaching and weapon smuggling. While these charges were dismissed, in the process of defending himself against them Reid-Daly verbally attacked Major General John Hickman. For this he was charged with insubordination and sentenced with a reprimand. Disgusted, he resigned as the commander of the Scouts in August, but continue to fight a legal battle against the judgement, proclaiming his innocence. This continued even after Rhodesia became Zimbabwe, and only stopped after Reid-Daily moved to South Africa in 1982.
In South Africa, Reid-Daly became commander of the Transkei Defence Force, and later was the leader of the private security firm Security Services Transkei Pty Ltd. He currently lives in South Africa.