Stephen Roskill was born in London on 1 August 1903, the son of John Henry Roskill and Sybil Mary Wentworth Dilke. He was educated at Mr Egerton's School, 13 Somerset Street, London; Horris Hill School, Newbury, 1911-16; and the Royal Naval Colleges at Osborne and Dartmouth, 1917-20. He married Elizabeth Van den Bergh in 1930, with whom he had four sons and three daughters.
He served as a Midshipman in the cruiser HMS Durban on the China Station, 1921-4, and also acted as a research assistant to Lieutenant-Commander Stephen King-Hall, who was writing a book on East Asia and Western civilization. He was promoted Sub-Lieutenant and Lieutenant and served in the sloop HMS Wistaria on the North American and West Indies Station, 1925-6, and HMS Ramillies on the Home and Mediterranean Stations, 1927. He also spent some time as a German Language Officer at Freiburg-im-Breisgau, 1926-7. He was a student on the long gunnery course at the Royal Naval College, Greenwich, and HMS Excellent, 1927-9, and then joined the instructional staff at HMS Excellent, 1929-30. He served as a gunnery officer in the battleship HMS Royal Sovereign, 1930-2, the aircraft carrier HMS Eagle, 1933-5, and the battleship HMS Warspite, 1936-9, and returned as a gunnery instructor to HMS Excellent, 1935-6. He was promoted Commander, 1938; joined the Admiralty staff, 1939-41; and was then posted to the cruiser HMNZS Leander in the Pacific, 1941-3, which he later commanded as Captain, 1944. He was chief staff officer for administration and weapons in the British Admiralty Delegation in Washington, 1944-5; senior British observer at the Bikini Atoll atomic bomb tests, 1946; and Deputy Director of Naval Intelligence at the Admiralty, 1947-8. He retired from the Navy in 1948, due to increasing deafness caused by exposure to gun detonations.
Following his retirement, he pursued a career as a historian. He was official naval historian of the Second World War in the Cabinet Office Historical Section, 1949-60, and a Senior Research Fellow, 1961-70, and Pensioner Fellow, 1970-82, at Churchill College, Cambridge, where he was closely involved in the early development of Churchill Archives Centre.
He died in Cambridge on 4 November 1982.
He was awarded the DSC, 1944, and CBE, 1971.
His publications include: "Claude Francis Webster" (1945); "The War at Sea 1939-1945", three volumes (1954, 1957, 1960-1); "Escort, the Battle of the Atlantic" (1955); "HMS Warspite" (1959); "The Secret Capture" (1959); "The Navy at War" (1960); "The Strategy of Sea Power" (1962); "A Merchant Fleet in War" (1962); "The Art of Leadership" (1964); "Naval Policy Between the Wars", two volumes (1968, 1976); editor, "Documents Relating to the Naval Air Service" (1969); "Hankey, Man of Secrets", three volumes (1970, 1972, 1974); "Churchill and the Admirals" (1977); and "Admiral of the Fleet Earl Beatty, the Last Naval Hero" (1980).
Papers comprising diaries, correspondence, manuscripts of books, articles, lectures, broadcasts, preparatory notes, copies of original papers used in research, card indexes, subject files for the official naval history of the Second World War, press cuttings, microfilms and photographs.
The papers were given to Churchill Archives Centre by Stephen Roskill in a number of accessions between 1966 and 1975. Further papers were added by his executors, 1983; his daughter, Tessa Till, 1983; his son, Nicholas Roskill, 1990 and 2014; Commander Geoffrey Hare, 1983; Collins Publishers, 1983; Professor Clark G. Reynolds, 2001; and his daughter, Mary Caroe, 2014.
Many of Stephen Roskill's earlier papers were destroyed by fire, 1931, and bomb damage, 1940, at the family home in London.