Brown was first elected as Liberal MP for Rugby 1923-24. He was returned to the House of Commons at a by election at Leith in 1927, following the resignation from the party of William Wedgwood Benn. In parliament, Brown was increasingly associated with Sir John Simon and took the Liberal National whip in 1931. In 1940 he succeeded Simon as leader of the Liberal Nationals and lead the party until his defeat in the 1945 general election. He held a series of government and cabinet posts in the National and wartime coalition governments, including Minister of Labour and Minister of Health.