Sir Felix Maximilian Schoenbrunn Cassel, 1st Baronet, PC, QC, JP (16 September 1869 – 22 February 1953) was a German-born British barrister and politician who served as Judge Advocate-General, the senior civilian lawyer of the War Office (and later also the Air Ministry) responsible for the administration of courts-martial, from 1915 to 1934.
Cassel was born into a Jewish family in Cologne, Germany. His father was Louis Schoenbrunn Cassel and his uncle was the philanthropist Sir Ernest Cassel. He was educated at Elstree School and Harrow School (1883–1888), and won a scholarship to Corpus Christi College, Oxford, where he obtained firsts in classical mods in 1891 and jurisprudence in 1892.
He was called to the Bar at Lincoln's Inn in 1894 and took silk in 1906, practising in Chancery. He became a bencher of Lincoln's Inn in 1912 and treasurer in 1935.
In 1907, he was elected to London County Council as Municipal Reform Party member for West St Pancras, serving until 1910. In the December 1910 general election, he was elected to the House of Commons as Conservative member for St Pancras West, a seat he held until October 1916, when he resigned it by talking the Chiltern Hundreds. He had previously been defeated standing for Hackney Central in the January 1910 general election.