Merlin was the only child of Sir David John Montagu-Douglas Scott, K.C.M.G., O.B.E., and his wife, Dorothy Charlotte Drummond. He was born at Boughton House, near Kettering, Northamptonshire, the residence of his grandfather, a son of the 5th Duke of Buccleugh. His mother was descended from the founders of Drummonds Bank, The Drummonds lived at Enderby Hall, Leicester.

He was educated at Eton and Matriculated in 1938. He was up at Christ Church for only one year.

He was gazetted to the Rifle Brigade on 9 January 1940 and was serving with the 2nd Battalion with the rank of Second Lieutenant, when he was killed at Halfaya on 9 May 1941.

He is buried at Halfaya Sollum War Cemetery Plot 1. D. 1.

His obituary notice in The Times on 10 May 1941, requested “No letters”.

The parish magazine for Enderby reported in 1941,
“In July Lady Scott, a sister of Mr. Drummond, has recently received news that her only son, 2nd/lieut. Merlyn Montagu-Douglas-Scott, of the Rifle Brigade, has been killed in action in the Middle East”.