Bruce served in the Territorial Army from 1931 to 1935, later in World War II, in the Royal Signals, where he reached the rank of Major in 1942,[2] serving in the anti-aircraft defence of London before joining Dwight D. Eisenhower's staff as an Intelligence Officer in the preparations for D-Day for which he won a mention in dispatches.

From 1945 to 1950 Bruce was Labour Member of Parliament (MP) for Portsmouth North.

[3] During the same time he was Parliamentary Private Secretary to the Minister of Health Aneurin Bevan, and compiled many notes and documents with the aim of writing a biography of Bevan, a task later taken up with the assistance of Bruce's papers by Michael Foot.

On 20 January 1975, he was created a life peer as Baron Bruce of Donington, of Rickmansworth in Hertfordshire.

Lord Bruce of Donington was married twice, firstly to Joan Letitia Butcher in 1939, and after their divorce in 1980, secondly to Cyrena Heard (née Shaw) in 1981.