James Somerville was born in Weybridge, Surrey, 17 July 1882, the son of Arthur Fownes Somerville and Ellen Sharland. He married Mary Kerr Main in 1913 (died 1945), with whom he had one son and one daughter.

He entered the Royal Naval College, Dartmouth, 1897. He was appointed Midshipman to the battleship HMS Magnificent, 1898, and over the next few years served in several ships on the Home, Mediterranean, Pacific and China Stations. He was promoted Lieutenant, 1904, and joined HMS Vernon, 1907, qualifying as a torpedo specialist with a particular interest in the new field of wireless telegraphy. He was promoted Lieutenant-Commander, 1912, served as a wireless officer in various ships, and took part in the Dardanelles campaign, 1915. He was promoted Commander, 1915, and Captain, 1921; commanded the battleships, HMS Benbow, HMS Barham and HMS Warsprite, 1923-9; and was Director of the Signal Division at the Admiralty, 1925-7. He was an instructor at the Imperial Defence College, 1929. In 1931, he and Captain John Tovey conducted an enquiry into the Invergordon mutiny. He assumed command of the cruiser HMS Norfolk and was then appointed Commodore of the naval barracks at Portsmouth, 1932-3. He was promoted Rear-Admiral, 1933, and returned to the Admiralty to become Director of Personal Services, 1934. He became Rear-Admiral (Destroyers), Mediterranean Fleet, 1935, and, following the outbreak of the Spanish Civil War in 1936, spent the next two years as senior British naval officer off the Mediterranean coast of Spain. He was promoted Vice-Admiral, 1937, and became Commander-in-Chief, East Indies, 1938, but was forced to retire due to ill health, 1939.

During the Second World War, he worked first as a radio commentator on the war and then at the Admiralty's request toured the country to oversee the development and installation of naval radar on ships, 1939-40. He volunteered to assist Admiral Ramsay at Dover during the evacuation of Dunkirk, May-June 1940. Later in 1940, he was placed in command of Force H, a squadron based in Gibraltar, whose first mission was to destroy the French Fleet at Mers el-Kebir, in Algeria. Force H was active in the western Mediterranean, escorting convoys into the mid-Atlantic and re-supplying Malta, 1940-1. One of its most notable actions was the pursuit of the Bismarck in May 1941. He was promoted Admiral and appointed to command the Eastern Fleet, 1942-4. He headed the British Admiralty Delegation in Washington, 1944-5, and was promoted Admiral of the Fleet on VE Day 1945.

He retired to his family home at Dinder, in Somerset, 1946, and died on 19 March 1949.

He was awarded the DSO, 1916; CB, 1934; KCB, 1939; KBE, 1941; GCB, 1944; GBE, 1945.