Fisher was a tutor in modern history at the University of Oxford. His publications include Bonapartism, The Republican Tradition in Europe and Napoleon. In September 1912, he was appointed as a member of the Royal Commission on the Public Services in India of 1912–1915. Between 1913 and 1917 he was Vice-Chancellor of the University of Sheffield. In December 1916 Fisher was elected Member of Parliament for Sheffield Hallam and joined the government of David Lloyd George as President of the Board of Education. He was sworn of the Privy Council the same month. In this post he was instrumental in the formulation of the Education Act 1918, which made school attendance compulsory for children up to the age of 14. Fisher was also responsible for the School Teachers Act 1918, which provided pension provision for all teachers. In 1918 he became MP for the Combined English Universities. Fisher resigned his seat in parliament through appointment as Steward of the Chiltern Hundreds on 15 February 1926, retiring from politics to take up the post of warden of New College, Oxford, which he held until his death. There he published a three-volume History of Europe in 1935. He served on the British Academy, the British Museum, the Rhodes Trustees, the National Trust, the Governing Body of Winchester, the London Library and the BBC. He was awarded the 1927 James Tait Black Memorial Prize for his biography James Bryce, Viscount Bryce of Dechmont, O.M. and received the Order of Merit in 1937. In 1939 he was appointed first Chairman of the Appellate Tribunal for Conscientious Objectors in England and Wales. Fisher died in St Thomas's Hospital, London, on 18 April 1940 after having been knocked down by a lorry and seriously injured the previous week, while on his way to sit on a Conscientious Objectors' Tribunal during the blackout. Some of his possessions, including his library and some of his clothing, remained at New College. In 1943, Operation Mincemeat, a British Intelligence operation to deceive enemy forces, undertook the invention of a false Royal Marines officer, whose body was to be dropped at sea in the hope the false intelligence it carried would be believed. As the fictitious Major Martin was to be a man of some means, he required quality underwear, but with rationing this was difficult to obtain, and the intelligence officers were unwilling to donate their own. Fisher's was obtained, and the corpse used in the deception, dressed in Fisher's quality woollen underpants, succeeded in misleading German Intelligence.
Family
Fisher married the economist and historian Lettice Ilbert in 1899. Their only child was the British academic Mary Bennett.