She was the only one of the class to serve in the Mediterranean fleet instead of the China station until returning to the Channel fleet in 1906 and in that year went into refit to receive Fire control. Further refitting was done while with the reserve at Portsmouth with reduced crew in 1908 - 09; on returning to the fleet she served as the parent ship for the 4th Division at the Nore and with the home fleet from May 1912 and again refitted at Chatham dockyard.
In 1913 HMS Canopus was stationed at Pembroke, Wales and at the outbreak of the First World War joined the 8th battle squadron of the Channel fleet, soon after she was sent to East Africa and the Cape of Good Hope. Late in 1914 she was attached to Sir Christopher Cradock's squadron which went in search of Admiral Maximilian von Spee's East Asian Squadron in the south-eastern Pacific Ocean. Canopus 's slow maximum speed of only 17 knots meant that she was 300 miles south of the rest of Cradock's squadron when he fatally engaged the German force at the Battle of Coronel on 1 November 1914. She then made for Port Stanley in the Falkland Islands, where she was grounded as a local defence fortress. On 8 December 1914 she fired the opening shots of the Battle of the Falkland Islands at extreme range (12,000 yards), even though her rear guns were only loaded with practice shots -- one of these shots ricocheted off the water and struck SMS Gneisenau, which fortunately persuaded the German force to break off their attack on the Falklands' radio and coaling stations thus allowing the British force which had arrived at Stanley only the previous day to raise steam and pursue the German force to its destruction. If Canopus had not driven off the German cruisers, the British force would have been caught in harbour, and the outcome of the battle could have been very different.
In February 1915 she was sent to the Mediterranean to support the Dardanelles expedition. While there she was damaged by Turkish gunfire on the 28 April and on 2 May 1915 she was involved in a grounding off Gaba Tepe. In October 1915 she transported troops to Salonika. On returning back to Britain she became the guard ship on the East Coast until 1918 when she was sent to Devonport, where she became a accommodation ship until being sold to the breakers in 1920.