Brian O’Brien was born in Formby, Lancashire on 31 March 1907, the son of Colonel Eoghan O’Brien, DSO and Frances Victoria Lucy O’Brien (née Smythe). Midshipman (E) O’Brien was appointed to the RN Engineering College, Keyham on 14 January 1926 and was promoted to Sub Lieutenant (E) on 1 March 1928. Promotion to Lieutenant (E) followed on 1 March 1930. He was appointed to the cruiser HMS CUMBERLAND on 18 March 1931.

O’Brien was appointed to HMS DOLPHIN for submarine training on 9 May 1932, and, on 7 April 1933 he was appointed to HMS PERSEUS as Engineering Officer. He was appointed as assistant to the Naval Overseer at Vickers at Barrow on 14 July 1936. He was promoted Lieutenant Commander (E) on 1 March 1938 and appointed to HMS THAMES as Engineering Officer on 10 January 1939. HMS THAMES was lost with all hands and is assumed to have been mined in the North Sea on 3 August 1940.

Brian O’Brien was the husband of Elizabeth O’Brien (née Strahan) from Bentley in Hampshire. He is commemorated on the Portsmouth Naval Memorial on Panel No. 37 Column No. 1.