In 1820, Duncombe ran for Parliament for Pontefract as a Whig candidate. He lost. In 1823, he ran again as a Whig for Hertford and was again unsuccessful. In June 1826, Duncombe finally won a seat in Parliament for Hertford. He enjoyed a great success in the Commons with two early speeches in which he vigorously attacked the Government. According to Greville, however, he had merely committed to heart and rehearsed speeches which had been prepared for him by Henry de Ros. Greville noted caustically in his diary for 25 February 1828: