Derek was the only child of Barret Lennard Albemarle O'Malley and his wife Lorna Josephine Coleridge and was born at 14A Northcote Avenue, Ealing. At the time of the 1911 census, his father was a journalist on the Morning Post. In the 1929 election, he stood as the Liberal candidate in the Lewisham constituency.

Derek was educated at Westminster and Matriculated in 1929 having won a Westminster Scholarship to Oxford. His parents were living at 24 Marlborough Road, Richmond, Surrey. After going down, he read for the Bar.

He was gazetted as a Pilot Officer on 11 November 1938.

Soon after the outbreak of war, he married Rachel Mary Genevieve Macdonald at Henley. Their son was born the following summer.

He was with 264 Squadron when on 4 September 1940, he was flying a Bouton Paul Defiant which crashed at 21.30 whilst attempting a night landing at Kirton-in-Lindsey, Lincolnshire

He is buried at Kirton-in-Lindsey along with Sgt. Laurie Andrew Woodney Rasmussen of the New Zealand Air Force who was killed with him. Block A. Grave 181.

Administration of his estate was granted to his widow. He left £1065-0-11.

His father wrote to the College after his death.

Rachel O’Malley continued to live in Henley and had a spacious flat at 10 Royal Mansions near the railway station. She took in crews during the Regatta “where they slept half a dozen to a room and were fed splendidly”. She would be a bit scathing about their lack of success “On her grand piano was her violin and a copy of the fiercely difficult Wieniawski concerto”. Her brother, Andrew David MacDonald, also a graduate of Christ Church, was killed on 16 February 1945. She died in Henley in 1982.

Derek’s son and six grandchildren are graduates of Oxford. His son and a grandchild were undergraduates at Wadham, two grandchildren were at New College. The others were at Balliol, Magdalen and Oriel.