Duncan was born in Kensington on 5 April 1924, the younger son of Sir Denis Duncan Harold Owen Boulton 3rd Bt and his wife Louise McGowan.
He matriculated in 1942 and was a Lieutenant in the 1st (Motor) Bn Grenadier Guards when he was killed at Monte Cassino on 9 February 1944. He was, originally, listed as Missing.
He is commemorated on Panel 3 of the Cassino Memorial.