Mackay Hugh Baillie Scott, Jnr. was born in Douglas, Isle of Man on 13 May 1891. He was the son of the architect Mackay Hugh Baillie Scott (1864-1943). By 1911 he had moved with his family to Bedford in Bedfordshire. Nothing is known about his training as an architect. This may have come from his father. During World War One he served as a lieutenant in the Royal Naval Volunteer Reserve. By 1926 he was living in London.
During the 1920s he appeared to have worked in Hong Kong. A bungalow in Hong Kong designed by him is illustrated in Recent English Domestic Architecture 1929, edited by H. de Hastings (1929 p.93). His address was given as Ockhams, Sevenoaks, Kent in 1939, and Kensington Palace Mansions, De Vere Gardens, Kensington, London in 1943. He died in Westminster, London 9 February 1943.