After being brought up in India and then the UK, where he attended preparatory school at Margate, he joined the Royal Navy as a cadet in the training ship HMS Britannia on 15 July 1885.
A born leader and fighter, full of dash, aggressive and fearless almost to the point of endangering sound judgment, Keyes quickly earned the devotion of all who served under him. From 1905 to 1908 he was stationed in Rome as naval attaché in the grade of captain; five years later, he was inspecting captain of submarines and in August 1912, commodore in charge of the submarine service.
For the first six months of the Great War, Keyes was responsible for submarine warfare in the North Sea, and late in August 1914, he took part in the action in the Helgoland Bight in which Admiral David Beatty's battle cruisers surprised and destroyed three German light cruisers off Helgoland Island; Keyes rescued 220 of the crew of the Mainz during that action.
In February 1915, Keyes was assigned chief of staff to Admiral Sackville Carden in command of the naval squadron at the Dardanelles, and one month later, after Carden's retirement owing to ill health, he became chief of staff to Carden's successor, Admiral De Robeck. In this capacity Keyes played a prominent role in planning the naval as well as the military operations in this theater of the war. Although the great naval attempt to force the Straits on March 18 failed, Keyes remained "coldly confident” that the operation could yet be brought to a swift and successful conclusion. When army General Sir Charles Monro in October 1916 counseled immediate evacuation of the Allied troops beached at Gallipoli, Keyes urged De Robeck to attempt yet another naval assault upon the Straits. De Robeck, however, regarded the risks of further naval operations as out of all proportion to the possible gains. This notwithstanding, he allowed his chief of staff to plead his case in London. Lord Kitchener found Keyes to be "a very pertinacious young man," and agreed at the request of the government to undertake a personal tour of the Dardanelles and to report on the situation at the narrows. Kitchener's negative evaluation ended all further offensive actions in this theater. According to De Robeck, the soldiers at Gallipoli referred to Keyes openly as the "lunatic sailor."
From June 1916 to June 1917, Keyes commanded the battleship Centurion in the Grand Fleet and, upon promotion to the grade of rear admiral, was placed in charge of the fourth battle squadron. In October 1917, he was recalled to the Admiralty as director of plans, and in this capacity turned his attention to possible naval operations against the enemy submarine lairs at Zeebrugge and Ostend. Keyes got the chance to put his theory into practice in January 1918 when, after promotion to vice admiral, Dover Patrol, this master of narrow-seas warfare came up with a bold design to block the two captured Belgian ports. Specifically, Keyes planned to block Ostend by sinking two old cruisers in the channel under cover of a smoke screen; at Zeebrugge, where a mole housed powerful shore batteries, he opted to land a party of marines under cover of smoke to silence the German guns, and to blow up an old submarine loaded with explosives under the viaduct leading to the mole, thus preventing the enemy from bringing up reserves, while another three superannuated cruisers would be sunk in the canal entrance. The operation was carried out on April 22, 1918, with Keyes on board the Warwick. Zeebrugge was a complete success, but at Ostend the blockships failed to reach their destination because the Germans had moved a buoy. Nevertheless, the audacity of the plan received worldwide attention even though the Germans cleared the channel in a few hours. As Marder has aptly put it: "The psychological effect was con-siderable; the strategic, almost nil."
After the war, Keyes was created a baronet and given a grant of £10,000. He commanded the battle cruiser squadron in 1919-21, and next served as deputy chief of the naval staff in the Admiralty in the grade of vice admiral. In 1925 he was appointed commander in chief, Mediterranean Fleet, reaching the grade of admiral the following year; in 1929 he was commander in chief, Portsmouth, and promoted to admiral of the fleet. Keyes was placed on the retirement list in May 1935. On May 7, 1940, he took a decisive role in the debate in the House of Commons that led to the resignation of Prime Minister Neville Chamberlain. Next came duty as liaison officer to King Leopold III of Belgium, and in 1940 Keyes was instrumental in the creation of the famous "commandos." In 1943 he was raised to the peerage as Baron Keyes, of Zeebrugge and of Dover. He died on December 26, 1945, at Buckingham. Winston Churchill said of him: "In many ways his spirit and example seemed to revive in our stern and tragic age the vivid personality and unconquerable dauntless soul of Nelson himself."
In 1906 Keyes married Eva Mary Bowlby: they had two sons and three daughters including Geoffrey Keyes, who was killed in action in 1941 and was posthumously awarded the Victoria Cross.