Edward Howard Marsh (known as "Eddie") was born on 18 November 1872, the son of Frederick Howard Marsh and Jane Marsh (née Perceval). Marsh was educated at Westminster School and at Trinity College, Cambridge.

Marsh entered the Colonial Office as a 2nd Class Clerk in 1896 where he was Assistant Private Secretary to Joseph Chamberlain (1900) and to Alfred Lyttelton (1903). He had risen to the position of 1st Class Clerk when he became Private Secretary to Winston Churchill in 1905, accompanying him on his visit to East Africa and Uganda (1907-1908). Marsh became Assistant Private Secretary to Herbert Asquith (1915-1916) before serving as Private Secretary to Churchill again from 1917-1922 and 1924-1929 (at the Board of Trade 1908-10, the Home Office 1910-11, the Admiralty 1911-15, the Duchy of Lancaster 1917, the War Office 1917-21, Colonial Office 1921-24 and the Treasury 1924-29). He was Private Secretary to the Duke of Devonshire (1922-24) and to J. H. Thomas (1924 and 1929, and 1936), and to Malcolm MacDonald (1936-1937).

Marsh retired from the civil service in 1937 and became Trustee of the Tate Gallery (1937-44), Chairman of the Contemporary Art Society (1937-52) and Vice-President of the Royal Society of Literature in 1943. In addition to his civil service career, Marsh was also an important patron of the arts. He had an extensive art collection and was also a strong supporter of poets such as Rupert Brooke, editing "Georgian Poetry" from 1912-21. His other published works include his Memoir of Rupert Brooke (1918) and translations from French and Latin including "Fables of La Fontaine" (1931) and "Odes of Horace" (1941). His memoirs were published as "A Number of People" (1939). Marsh also played an important role in Churchill's literary projects, ranging from proof-reading and commenting on Churchill's work to drafting newspaper articles for him.

Marsh was unmarried and died on 13 January 1953.