He was promoted to temporary lieutenant in the Grenadier Guards on 15 November 1914, later with seniority from 3 November 1914, and became a substantive lieutenant on 11 November 1914. On 29 January 1916, he was made a supernumerary temporary captain with the Guards, relinquishing the rank on 12 May 1916. Lord Stanley was appointed adjutant of the newly formed Household Battalion on 9 September 1916, again as a temporary captain. He received a substantive captaincy on 26 September 1916 and served as adjutant until 12 January 1917. He was appointed a staff captain and seconded on 13 August 1917, and made a brigade major on 22 January 1918, a post he held until 11 March 1918. He served as a general staff officer, 3rd grade, from 6 May 1918 to 8 October 1918. On 9 October 1918, he was again appointed a brigade major. serving in that capacity until 2 November 1919. Lord Stanley was awarded the Military Cross on 3 June 1919, for his service in Italy. On 27 November 1920, he retired from the Army and entered the reserve of officers as a captain. Lord Stanley was first elected to Parliament on 28 June 1917 in a by-election in Liverpool Abercromby. He left Parliament the following year, when the seat was abolished for the 1918 general election. During this time, he was the Baby of the House. He returned to Parliament in the 1922 general election when he was elected for Fylde. He served under Stanley Baldwin as a Junior Lord of the Treasury from 1924 to 1927 and was a Deputy Chairman of the Conservative Party from 1927 to 1929. On the formation of the National Government after the 1931, Stanley was made Parliamentary and Financial Secretary to the Admiralty under Ramsay MacDonald. On 26 February 1934, he was admitted to the Privy Council. In 1935 he was made Under-Secretary of State for Dominion Affairs by Baldwin, and later that year was made Parliamentary and Financial Secretary to the Admiralty. Two years later, Lord Stanley became Under-Secretary of State for India and Burma. On 16 May 1938 he entered the cabinet as Secretary of State for Dominion Affairs. His brother, Oliver, was also in the Cabinet as President of the Board of Trade. However, in October 1938, five months after being appointed to the cabinet, Lord Stanley died in Marylebone, aged 44. Neville Chamberlain paid tribute to him in the House of Commons: "So great, indeed, was his keenness and his interest in Imperial relations that he insisted on carrying out his intention to visit Canada, although even then he was suffering from the disease which has now ended fatally.