She was ordered under the 1911 Naval Estimates and built in the yards of William Beardmore and Company, of Glasgow. She was laid down on 30 May 1912 and launched on 12 November 1913. She was commissioned in October 1914 after the outbreak of the First World War .
She served during the First World War as part of the Grand Fleet, and led one of the squadrons of the Fleet in the major naval engagement of that war, the battle of Jutland in 1916. She spent the rest of the war in home waters, but was dispatched to the Mediterranean after the end of the war, and then into the Black Sea. Here she carried out a number of shore bombardments in support of the White Russians in the Russian Civil War, until their collapse in 1920. She remained with the Mediterranean Fleet until 1926, when she returned to the Atlantic Fleet. She was decommissioned in 1929, disarmed under the terms of the London Naval Treaty in 1930 and was sold for scrapping in 1931.
A more radical departure was the replacement of the guns of the secondary armament with twelve guns. These made Benbow more capable of engaging the larger destroyers and torpedo boats then being built. Admiral of the Fleet Jackie Fisher had been opposed to mounting such heavy weapons on the grounds of economy, and because he believed they would be rendered useless in bad weather. He had retired by the time the class were being designed, but the guns were still heavy for a secondary armament and so they were mounted low in casemates. This had the predicted effect of often rendering them unusable in poor weather. Attempts were made to alleviate the situation including mounting Benbow’s as far back as possible to help reduce wetness but met with limited effectiveness. Benbow’s guns were fitted in casemates, with five either side of the forecastle deck and two right aft in the hull below the quarter deck, rather than in the deck houses, as had been the practice before. The two stern guns were subsequently found to be so wet as to be useless. They were re-sited on the forecastle deck, but the forward batteries continued to swamped in heavy seas. Eventually rubber sealing joints for the gun ports were designed and fitted at Scapa Flow to try to alleviate the situation. The fitting of the larger guns made Benbow longer, wider and deeper and 2,000 tons heavier than previous classes.
She was also armed with two anti-aircraft guns on her after superstructure in 1914, making the class the first British battleships to carry anti aircraft guns. Benbow carried four submerged torpedo tubes mounted along her sides, but unlike preceding classes, she did not carry a stern mounted torpedo tube. Her total broadside was ten guns, six guns and two torpedoes.
She also had heavy tripod masts fitted to enable the addition of fire direction equipment. Compared to the preceding King George V class, Benbow’s funnels were taller and thinner which made her distinctive. Unlike her sister, HMS Iron Duke, she was not fitted with anti torpedo nets, due to their effect in reducing the ship's speed.
Prior to the battle of Jutland, Benbow left Scapa Flow with the rest of the Grand Fleet under the command of Admiral John Jellicoe on 30 May 1916. She led the 4th Division, consisting of HMS Bellerophon, HMS Temeraire and HMS Vanguard. The 4th Division formed the column of ships immediately to starboard of the fleet flagship, the Iron Duke under Jellicoe as they steamed south eastwards to meet the German High Seas Fleet. At 1710 on 31 May, Benbow relayed a message to Jellicoe on the Iron Duke that the High Seas Fleet was at sea with 26-30 battleships on a course of 347 in line ahead. This indicated that the German Admiral was at sea with his full strength – 18 Dreadnought type battleships and ten pre-Dreadnoughts and that the two sides were on a converging course.
Benbow opened fire at 1830 with intermittent salvoes at the lead German battleships of the König class. Poor visibility led to her ceasing fire 10 minutes later, having fired just six two-gun salvoes from her forward turrets. By 1900, she had made a turn to starboard, leading the 4th division past the wreck of HMS Invincible which had been destroyed by a magazine explosion. The turn brought them towards the German fleet, and at 1909 she again opened fire with her batteries on the German destroyers of the 3rd flotilla at , believing them to be making a torpedo attack. They were actually attempting to rescue the crew of the German light cruiser Wiesbaden, which had been disabled earlier by HMS Invincible, and was now under fire from the Grand fleet. Benbow then shifted her fire to the 6th and 9th destroyer flotillas which had begun to launch torpedo attacks.
At 1917 Benbow opened fire on the Derfflinger with a two gun salvo from her forward turret. The shells passed over the ship and Benbow readjusted her aim down and swung about to allow her after gun to fire. She then fired four 5 gun and one 4 gun salvoes, claiming a single hit on the German cruiser, which was later disproved. She again ceased fire at 1924 due to poor visibility caused by the smoke laid by the German destroyers during their torpedo attacks. The High Seas Fleet disengaged and fled to the south. At 2010 there was a brief skirmish between the German destroyers V46 and V69, and the British 2nd Light Cruiser squadron and Benbow, in which Benbow fired a single salvo of shells and a single round from her B gun before the German ships escaped. This was the last contact with the enemy, and Benbow returned with the rest of the fleet to Scapa Flow. In total Benbow had fired 40 rounds of shells, all of them being "Armour Piercing capped" (APC), and 60 rounds of shells. She had mananged to escape damage or casualties.
She spent the remainder of the war at anchor at the 4th Division's home port of Scapa Flow, or on manoeuvres and routine patrols in the North Sea.
In 1919 Benbow was deployed in the Mediterranean, and then with the Black Sea squadron in support of the White Russians in the Russian Civil War. She carried out a number of shore bombardments, until she left the squadron in 1920. She became part of the Mediterranean fleet until 1926. Benbow’s captain between 1921 and 1923 was James Fownes Somerville, later Sir James Fownes Somerville, Admiral of the Fleet.
Benbow left the Mediterranean in 1926 and joined the Atlantic Fleet until 1929, when she was paid off into reserve. She was disarmed in 1930 under the terms of the London Naval Treaty and placed on the disposal list. Benbow was sold for scrap in January 1931 and scrapped in March 1931 by Metal Industries, of Rosyth.