She stood unsuccessfully as the Labour Party candidate for Islington East in the General Elections of 1922 and 1923. Bentham was finally successful in the 1929 general election, the fifteenth woman MP, the first ever woman Quaker and doctor, and at 68 years of age the oldest woman to be elected to Parliament. This coincided with the election of the second ever Labour Government headed by Ramsay MacDonald. She spoke only infrequently in the House of Commons in her two years in Parliament. One of her longest speeches was during debate on the Mental Treatment Bill.