Following the outbreak of the First World War, Caesar returned to the Channel Fleet before being transferred to the North America and West Indies Station in 1915 after a brief spell as a guard ship at Gibraltar.

Her propulsion system consisted of two 3-cylinder triple-expansion steam engines powered by eight coal-fired, cylindrical fire-tube Scotch marine boilers.

[2] The ship was armed with a main battery of four BL 12-inch (305 mm) Mk VIII guns in twin-gun turrets, one forward and one aft.

She was also equipped with five 18 in (457 mm) torpedo tubes, four of which were submerged in the ship's hull on the broadside, with the last in a deck-mounted launcher on the stern.

[1] The barbettes for the main battery were protected with 14 in (356 mm) of armour, and the conning tower had the same thickness of steel on the sides.

[3] In May 1898, Caesar departed the United Kingdom for her Mediterranean service under the command of Captain Edward Harpur Gamble.

[6] Her refit completed, Caesar was commissioned at Portsmouth on 2 February 1904 to relieve her sister ship HMS Majestic as flagship of the Channel Fleet.

[6] In May 1909, Caesar transferred to the Nore, temporarily serving as the flagship of Vice Admiral, 3rd and 4th Divisions, Home Fleet.

[6] In March 1912, Caesar was placed in commissioned reserve with a nucleus crew as part of the 4th Division, Home Fleet.

In 1918 she was the flagship of Rear-Admiral Sir Morgan Singer, second-in-command, North America and West Indies Station (to Vice-Admiral Sir William Lowther Grant, the Commander-in-Chief, North America and West Indies Station), and Admiral Superintendent, Bermuda.

[8][7] Her North America and West Indies Station service ended in September 1918, when Caesar was transferred to relieve HMS Andromache (the old second-class cruiser and former minelayer HMS Latona) as flagship of the Senior Naval Officer, British Adriatic Squadron, at Corfu, the last British pre-dreadnought to serve as a flagship.

In June 1919, Caesar transited the Dardanelles and transferred to the Black Sea, where she served as a depot ship for British naval forces operating against the Bolsheviks during the Russian Revolution.

Caesar returned to the United Kingdom in March 1920, paid off at Devonport on 23 April 1920, and was placed on the disposal list.