Between the two World Wars, he was General Secretary of the National Council of Social Service (1919–1937) and then Secretary of the National Fitness Council (1937–1939). In the 1950s he was an Associate Warden of Toynbee Hall.
Born in Nottingham, in 1916 Ellis was commissioned into the Welsh Guards from the Inns of Court Officers' Training Corps and saw service in the First World War. Ellis was awarded a Military Cross "for conspicuous gallantry and resource" while leading an attack under machine-gun fire and rose to the rank of captain. In 1919 he was awarded the Distinguished Service Order for gallantry and devotion to duty, in the advance south of Bavai. He returned to civilian life and became the first General Secretary of the new National Council of Social Service, a position he held from 1919 to 1937, then the first Secretary of the new National Fitness Council, 1937 to 1939, working with Lord Aberdare, the first chairman. In the 1930 Birthday Honours, Ellis was appointed a Commander of the Order of the British Empire "for services in connection with the Coalfields Distress Fund" and in 1937 a Commander of the Royal Victorian Order.
On 18 September 1939, shortly after the beginning of the Second World War, Ellis returned to the Welsh Guards and was later appointed as an official historian, contributing three volumes to the History of the Second World War. After the war, he was an Associate Warden of Toynbee Hall.
His The War in France and Flanders (1954) begins with the Phoney War of 1939–1940 and deals with the failed attempts of the British Expeditionary Force to defend Belgium and France from the German invasion of May and June 1940. It ends with the confusion of the Belgian surrender, the British failure to defend the Somme and the decision to evacuate British forces from Dunkirk. His later volumes dealt with the Normandy Campaign and the defeat of Germany.
In 1916, Ellis married Jane Richmond in the Southwark district and they had a son, Christopher St John Ellis (1920–1997), who served in the Royal Naval Volunteer Reserve during the Second World War and became a schoolmaster and also one daughter. Jane died in 1953 and Ellis died at Harlington, Middlesex, on 19 October 1970. Ellis was a painter and a friend of Rex Whistler, who was stationed with him during the Second World War.
- Welsh Guards at War (1946)
- History of the Second World War, United Kingdom Military Series: The War in France and Flanders 1939–1940 (London: HM Stationery Office, 1954)
- History of the Second World War, United Kingdom Military Series: Victory in the West: The Battle of Normandy by L. F. Ellis, with G. R. G. Allen, A. E. Warhurst, and Sir James Robb (London, H.M. Stationery Office, 1962)
- History of the Second World War, United Kingdom Military Series: Victory in the West: The Defeat of Germany (1968)
- The London Gazette (Supplement) dated 11 July 1916, p. 6932
- The London Gazette (Supplement) dated 2 December 1918, p. 14237
- National Archives, Medal card of Ellis, Lionel Frederic, ref. WO 372/6/195970
- The Edinburgh Gazette (Supplement) dated December 11, 1919, p. 3915
- Andrzej Olechnowicz, Working-class Housing in England Between the Wars: The Becontree Estate, (Clarendon Press, 1937), p. 142, footnote 38
- The London Gazette (Supplement) dated 3 June 1930, p. 3481
- The London Gazette (Supplement) dated 29 January 1937, p. 694
- The London Gazette (Supplement) dated 10 October 1939, p 6853
- Social Service: A Quarterly Review, Volumes 27-28 (1953), p. 1: "For the Well-Being of Mankind, Lionel F. Ellis, c.v.o., c.b.e., d.s.o. Associate Warden, Toynbee Hall".
- 'ELLIS, Lionel Frederic', in British Army Officers 1939–1945: A. A. Eagger to R. K. Exham at unithistories.com, accessed 22 July 2016
- Major Lionel Ellis CVO, CBE, DSO, MC at arts-and-crafts-company.com, accessed 23 July 2016
- L. F. Ellis, The War in France and Flanders, full text at ibiblio.org
- Ellis, Lionel Frederic (1885-1970), Major and military historian at National Archives