Marsh's father was Howard Marsh, a surgeon and later Master of Downing College, Cambridge. His mother was a granddaughter of the prime minister Spencer Perceval. He was educated at Westminster School and Trinity College, Cambridge, where he studied and was a member of the Apostles.
In 1905 he became Private Secretary to Winston Churchill (then Under-Secretary for the Colonies). He continued as Churchill's Private Secretary from then until 1929, in different government departments, except when Churchill was out of office. He received a knighthood on his retirement in 1937.
Marsh edited five anthologies of Georgian Poetry between 1912 and 1922, and became Rupert Brooke's literary executor, and edited Brooke's Collected Poems (1918).
- "[Rupert Brooke's] best friend at the end of his life was Edward Marsh, who was as much in love with him as [James] Strachey had been."
- http://janus.lib.cam.ac.uk/db/node.xsp?id=EAD%2FGBR%2F0014%2FEMAR "The Papers of Sir Edward Mars", Janus. Cambridge University.
- Keith Hale, Brooke, Rupert, in Claude J Summers (Ed.) The Gay and Lesbian Literary Heritage, Routledge, 2013