Born in Liverpool, she was educated at Liverpool and Oxford Universities. At Oxford she became, in 1931, the first woman president of the Oxford University Liberal Club. Balfour had a long and distinguished career as a journalist and broadcaster, starting her career at the Oxford Mail. She was a founding contributor to Picture Post and was the parliamentary correspondent for Time Magazine. From the 1930s onward she was a regular broadcaster on the BBC. In November 1941, Balfour became the founding secretary of the Liberal Action Group (later Radical Action). The group sought to energise the party and stimulate new ideas during the wartime political truce. In opposition to the truce she supported Independent Liberal candidates in by-elections at Chippenham and Bury St Edmunds. In 1943 Balfour temporarily resigned from the party to stand as an Independent Liberal in the Darwen by-election losing to the Conservatives by only 70 votes. In the 1945 general election she again stood in Darwen as the official Liberal candidate. After 1945 she became increasingly estranged with the Liberal Party and at the 1951 election publicly endorsed a number of Labour candidates. In 1957 she resigned from the party in protest at its selection of a pro-Suez candidate to fight the Carmarthen by-election.