Only son of Joseph Reid,[3] of 22 Elmwood Avenue, Belfast, he attended Queens College, Belfast and New College, Oxford, graduating with 1st Class Honours in History.[4] He then became a barrister at the Inner Temple[5] and was called to the Bar in 1898.[3] He contested East Tyrone in 1910 before becoming a Unionist Member of Parliament (MP) for East Down from 1918 to 1922, when the constituency was abolished. He was Chairman of the Ulster Unionist Party at Westminster.[6]
In 1936, when appointed Sheriff of Down, he was created a Baronet, of Rademon.[7] (Prior to his creation as a baronet, he was known as "D. D. Reid".) Upon his death the baronetcy became extinct.[citation needed]