By 1 May, "Monarch" had been assigned to the 3rd BS of the Home Fleet. On 1 November, the 3rd BS was disbanded and "Monarch" was transferred to the Reserve Fleet at Portland, together with her sisters. The ship had been transferred back to Portsmouth by 18 March 1920. She was temporarily recommissioned during the summers of 1920 and 1921 to ferry troops to the Mediterranean and back. On 5 May 1922, "Monarch" was paid off and placed on the disposal list in accordance with the terms of the Washington Naval Treaty. Put up for sale in August, the ship was later withdrawn and attached to the gunnery school at as a hulk.