Summerskill entered politics at 32 when she was asked to fight the Green Lanes ward in Harringay in the Middlesex County Council elections. She then served as a councillor on Middlesex County Council from 1934 until 1941. She stood for a seat in the House of Commons unsuccessfully at the Putney byelection in 1934 and Bury at the 1935 general election, before becoming Labour Member of Parliament (MP) for Fulham West at a by-election in 1938 thanks to the working women's vote. She caused some disquiet by taking the seat in her maiden name. When the Fulham West constituency was abolished for the 1955 general election, she was returned to the House of Commons as MP for Warrington.