In 1896 he was appointed Assistant Private Secretary to Joseph Chamberlain, the Colonial Secretary. When Chamberlain resigned in 1903, Marsh became Private Secretary to his successor, Alfred Lyttelton. When Winston Churchill became Under-Secretary of State for the Colonies in 1905 during Henry Campbell-Bannerman's first Government, Marsh became Churchill's Private Secretary, beginning an association and friendship that would last until Marsh's death. Marsh would be Churchill's Private Secretary for the next ten years, until Churchill left the Government in 1915. As Randolph Churchill put it, from December 1905, "Marsh was to accompany Churchill to every Government department he occupied: to the Board of Trade, the Home Office, the Admiralty, the Duchy of Lancaster, the Ministry of Munitions, the War Office, back to his original Colonial Office and the Treasury."Churchill, Randolph. Winston S. Churchill: Young Statesman 1901–1914. (c) 1967 C&T Publications, Ltd.: p. 110 The moves were somewhat irregular as Marsh remained, until 1937, officially a clerk at the Colonial Office, but many exceptions were made, possibly at a cost to Marsh's official advancement.
