At the 1708 British general election Lord Willoughby was returned as a Member of Parliament for Lincolnshire with his father's support. Although his father was a Whig, Willoughby acted as a Tory. He sat on a drafting committee for the Boston church bill, and a committee of inquiry into the laws excluding placemen. He acted against the Whigs in an electoral dispute. Although nominated to the committee examining the arrangements for the trial of Dr Sacheverell, he voted against the impeachment in 1710. He was returned as a Tory at the 1710 election and listed as one of the 'worthy patriots' who detected the mismanagements of the previous administration, and a 'Tory patriot' who opposed the continuation of the war in 1711. He was also a member of the October Club. He sat on drafting committees for bills to build a waterworks near Boston and to help drain the Ancholme Level. As a Hanoverian Tory, he voted against the expulsion of Richard Steele in March 1714. He did not stand at the 1715 general election but was summoned to the House of Lords by a writ of acceleration in his father's Barony of Willoughby de Eresby on 16 March 1715.