Nicholls began to practise law in January 1765, and became acquainted with John Dunning and later with Edmund Burke. On 15 Apr. 1782 Keppel recommended him to Rockingham for a seat in the House:
He is a Surrey gentleman of our principles, he does not want abilities in language and expression, was brought up to the law, but quitted business upon finding himself in an easy situation ... He is ready to spend money for a seat in Parliament, with only the reserve that if he should differ at any time, which he did not think the least likely to happen, he should in that case give up his seat.
He was returned in November 1783 for Sir Robert Clayton’s borough of Bletchingley as a supporter of the Coalition, and four days later voted for Fox’s East India bill. On 8 Dec. he spoke in defence of the bill, blaming the East India Company for ‘mismanagement’.
He thought the present ministers, destitute as they were of the confidence of the House of Commons, incapable of conducting the public business; the sooner they were removed, the sooner would the country be relieved from its present dangerous situation.
Later in life he recanted, writing:
He was again returned at the general election of 1784, and supported Opposition until 1786. The breach came over the impeachment of Hastings. Of Burke, Nicholls wrote: ‘At the commencement of our intercourse my admiration of him was very great; it gradually diminished into disapprobation of his measures, and disapprobation gradually increased into disesteem.’ Burke warned Nicholls that if he did not support the impeachment, he ‘must relinquish the friendship of the Duke of Portland’.
Nicholls spent the later years of his life in France, and in 1820 published his autobiography, Recollections and Reflections. He died in the spring of 1832.