He sat as a Member of Parliament for Boston, South Lincolnshire and Rutland and served as Lord Lieutenant of Lincolnshire.
While his appeal on petition to the elections committee of the House of Commons was upheld, the House held that the interference of his eldest brother, the Earl of Lindsey and Lord Lieutenant of Lincolnshire, had voided the election, and he again lost the subsequent by-election.
Lord Willougby inherited the earldom of Lindsey in 1701, and was invested a Privy Counsellor one month later; along with the Earldom of Lindsey, he also inherited the offices of Lord Great Chamberlain and Lord Lieutenant of Lincolnshire, both of which he would hold until his death and would pass onto his son, the 2nd Duke of Ancaster and Kesteven.
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