After the war Sassoon was involved in negotiating the terms of a pension and an earldom for Field Marshal Haig from the Prime Minister David Lloyd George in August 1919. The role of the private secretary was to undertake discreet discussions to prevent the need for Haig to submit direct correspondence. Lloyd George was so impressed that he went on to offer him a position as his own parliamentary private secretary in 1920.
Philip Sassoon was talented in combining deep knowledge and appreciation of art with impressive political skills. He entered Parliament as MP for Hythe in 1912, and between 1924 and 1929 and again from 1931 until 1937 he served as Under-Secretary of State for Air, and gained much prominence in political circles.