In the 1931 general election, Cripps was one of only three former Labour ministers to hold their seats and so became number three in the Parliamentary Labour Party, under the leader George Lansbury and deputy leader Clement Attlee. In 1932 he was one of the founders of the Socialist League, composed largely of members of the Independent Labour Party who rejected its decision to disaffiliate from Labour. The Socialist League put the case for an austere form of democratic socialism. Tall, thin and intense, he became the archetype of the British upper-class doctrinaire socialist so common in the 1930s.
In 1936 the National Executive Committee decided to dissociate itself from a speech in which Cripps said he did not "believe it would be a bad thing for the British working class if Germany defeated us". Cripps was an early advocate of a United Front against the rising threat of fascism. In 1936 he was the moving force behind a Unity Campaign, involving the Socialist League, the ILP and the Communist Party of Great Britain, designed to forge electoral unity against the right. Opposed by the Labour leadership, the Unity Campaign was a damp squib: Cripps dissolved the Socialist League in 1937 rather than face expulsion from Labour, though Tribune, set up as the campaign's propaganda organ and bankrolled by Cripps and George Strauss, survived (and survives to this day).
In early 1939, however, Cripps was finally expelled from the Labour Party for his advocacy of a Popular Front with the Communist Party and anti-appeasement Liberals and Conservatives. After the Hitler-Stalin pact Joseph Stalin instructed the Comintern to oppose anti-Hitler policies in other countries as an attempt to engineer an "imperialist' war".
In 1942 Cripps returned to Britain and made a broadcast about the Russian war effort. The popular response was phenomenal, and Cripps rapidly became one of the most popular politicians in the country, despite having no party backing. He was appointed a member of the War Cabinet, with the jobs of Lord Privy Seal and Leader of the House of Commons — perhaps a deliberate overpromotion by Churchill, as Prime Minister, designed to diminish his standing, as he was considered for a short period of time after his return from the Soviet Union as perhaps nearly a rival to Churchill in his hold on the country. Indeed, the London bureau chief of the Associated Press reported in American newspapers in early March 1942 the prediction by "an extremely well-placed and reliable political source . . . that there was every likelihood" that Cripps would soon unseat Churchill as prime minister. Instead, Churchill sent Cripps to India on what is known as the Cripps Mission to attempt to negotiate an agreement with the nationalist leaders Gandhi and Jinnah that would keep India loyal to the British war effort in exchange for a promise of full self-government after the war. No formal agreement was reached. For Churchill, the purpose of the trip was propaganda. Churchill intended Cripps to fail and blocked his efforts to give the Indians a role in the leadership of the war with the help of Linlithgow (William Roger Louis, "Ends of British Imperialism: the Scramble for Empire, Suez and Decolonization", Page 399). Later in 1942 he stepped down from being Leader of the House of Commons and was appointed Minister of Aircraft Production, a position outside the War Cabinet but in which he served with substantial success. In 1945 Cripps rejoined the Labour Party.
In 1946 Soviet jet engine designers approached Stalin with a request to purchase jet designs from Western sources in order to overcome design difficulties. Stalin is said to have replied: "What fool will sell us his secrets?" However, he gave his assent to the proposal, and Soviet scientists and designers travelled to the United Kingdom to meet with Cripps and request the engines. To Stalin's amazement, Cripps and the Labour government were perfectly willing to provide technical information on the Rolls-Royce Nene centrifugal-flow jet engine designed by RAF officer Frank Whittle, along with discussions of a licence to manufacture Nene engines themselves. The Nene engine was promptly reverse-engineered and produced in modified form as the Soviet Klimov VK-1 jet engine, later incorporated into the MiG-15 which flew in time to deploy in combat against UN forces in North Korea in 1950, causing the loss of several B-29 bombers and cancellation of their daylight bombing missions over North Korea.
In 1946, Cripps returned to India as part of the so-called Cabinet Mission, which proposed various formulae for independence to the Indian leaders. The other two members of the delegation were Lord Pethick-Lawrence, the Secretary of State for India, and A. V. Alexander, the First Lord of the Admiralty. However, the solution devised by the three men, known as the Cabinet Mission Plan, was unsatisfactory to the Indian National Congress (Gandhi is believed to have quipped that it was a "postdated cheque on a failing bank"), and India travelled further down the road which eventually led to Partition.
In 1947 amidst a growing economic and political crisis, Cripps tried to persuade Attlee to retire in favour of Ernest Bevin; however, Bevin was in favour of Attlee remaining. Cripps was instead appointed to the new post of Minister for Economic Affairs. Six weeks later Hugh Dalton resigned as Chancellor of the Exchequer and Cripps succeeded him, with the position of Minister for Economic Affairs now merged into the Chancellorship. Cripps laboured tirelessly to rescue Britain from its economic crisis. He increased taxes and forced a reduction in consumption in an effort to boost exports and stabilise the Pound Sterling so that Britain could trade its way out of its crisis. He strongly supported the nationalisation of strategic industries such as coal and steel.
Although Cripps' severe manner and harsh policies made him very unpopular, he won respect for the sincerity of his convictions and his tireless labours for Britain's recovery. His name once induced an infamous Spoonerism when the BBC announcer McDonald Hobley introduced him as 'Sir Stifford Crapps'.
Cripps was the nephew of Beatrice Webb. He was the father of children's author Peggy Cripps - who shocked much British opinion at the time by marrying a black African - and grandfather of her son, philosopher Anthony Appiah.
Cripps was a vegetarian, certainly for health reasons and possibly also for humanitarian/ethical reasons. "Cripps suffered from recurring illness which was alleviated by nature cure and a vegetarian diet....