Benn was elected as a Liberal Member of Parliament for the St George's division of Tower Hamlets in east London in 1906, holding the seat until 1918; his father had previously held the seat from 1892 to 1895. Between 1910 and 1915, he served in the Liberal government as a Lord of the Treasury. He was elected for Leith in Scotland in 1918. During the 1924–29 parliament, which was dominated by a Conservative majority, he worked closely with a group of radical Liberal MPs that included Frank Briant, Percy Harris, Joseph Kenworthy and Horace Crawfurd to provide opposition to the government. He sat until March 1927, when he resigned from the Liberal Party and from parliament. The following year he re-entered parliament as Labour member for Aberdeen North. Labour leader Ramsay MacDonald recognised his talent, and offered the possibility of promotion. Benn served as Secretary of State for India between 1929 and 1931 in MacDonald's second government, and was sworn of the Privy Council in 1929. However, he refused to follow MacDonald into the National Government coalition with the Conservatives, and at the 1931 election lost his seat to John George Burnett. He returned to parliament in 1937, when he was elected for Manchester Gorton. In 1940, following the internment of thousands of refugees under pressure from the military he spoke up for them in Parliament. In 1942, Benn was raised to the peerage as Viscount Stansgate, of Stansgate in the County of Essex. Two years later he was appointed Vice President of the Allied Control Commission which was charged with reconstructing a democratic government in Italy. In 1945 he became Secretary of State for Air in Clement Attlee's Labour government, a position he held until October 1946. He then sat as a backbench Labour peer until his death fourteen years later. From 1947 to 1957, Viscount Stansgate was President of the Council of the Inter-Parliamentary Union, the world organization of national parliaments. He first took up that office at the IPU's Conference in Cairo in April 1947, where he succeeded Count Henry Carton de Wiart of Belgium. A master in the art of human contacts, passionately interested in international politics, Viscount Stansgate played a major role in bringing the newly independent countries in Asia, the Middle East and Africa into the ranks of the IPU. He was also instrumental in re-establishing the membership of parliaments of Eastern European countries, thus bringing the IPU nearer to its traditional objective – universality.
A gallant observer of exceptional ability. After setting out on a bombing raid, the Scout machines assigned to act as an escort became separated, and it then became necessary for the bombing planes to proceed on their task without support. Captain Benn's machine took the lead, followed by three other bombers, and succeeded in dropping his bombs on an enemy aerodrome. On the return journey the bombing machines were attacked by several enemy scouts, which were eventually driven away. Recently, this officer organised and carried out a special flight by night over the enemy's lines, under most difficult circumstances, with conspicuous success. He has at all times set a splendid example of courage.
Also in September 1918 he and William George Barker flying an Savoia-Pomilio SP.4 aeroplane, specially equipped for a parachute drop. This was the first military parachute/spy mission. The parachutist was Alessandro Tandura, who parachuted behind enemy lines in the vicinity of the Piave river. In November, he was awarded the Bronze Medal of Military Valour by the Italian Government. After his return to politics, Benn resigned his commission in the RAF on 28 December 1918, retaining the rank of captain. Though in his early 60s at start of the Second World War, Benn returned to military flying, joining the Royal Air Force Volunteer Reserve as a war-substantive pilot officer on 27 May 1940, with the service number 79452. He was promoted to flying officer on 7 December, and was confirmed in his rank on 27 May 1941. Promoted in 1942 to the substantive rank of flight lieutenant, he was promoted to group captain on 29 December 1942, skipping two ranks. Following his promotion to acting air commodore in 1944, he served as Director of Public Relations at the Air Ministry. At the age of 67 he flew several flights operationally as an RAF Bomber Aircrew gunner, and is possibly the oldest man to have done so. He resigned his commission on 3 August 1945, retaining the rank of air commodore.
Family
Lord Stansgate married Margaret Holmes, daughter of Daniel Holmes, in 1920. His eldest son Michael Wedgwood Benn was killed in the Second World War in 1944. Stansgate died at Westminster, London, in November 1960, aged 83, and was succeeded in the viscountcy by his second son, then known as Anthony Wedgwood Benn, who was successful in 1963 in changing the law to allow him to disclaim the peerage for life. His youngest son, David Wedgwood Benn, a specialist in Russia and Eastern Europe, worked for the BBC's External Services for many years. A fourth son, Jeremy, was still-born.