During World War II, he served in the Royal Engineers in India and Burma and fighting his first election as candidate for Nelson and Colne in 1945 before demobilisation, also contesting Preston in a 1946 by-election.

He was a Lloyd's of London underwriter, a company director and chairman of Radio Luxembourg Ltd. Nicholls was Member of Parliament for Peterborough from 1950 to 1974, when he lost in the October election of that year to Labour's Michael Ward, having held on by just 22 votes in the election eight months earlier.

This was the second close call during his time as MP for Peterborough – in 1966, he held his seat by just three votes.

He was created a Baronet, of Darlaston in the County of Stafford, in 1960,[1] and in 1975, after he lost his seat in the House of Commons, he was given a life peerage as Baron Harmar-Nicholls, of Peterborough in Cambridgeshire,[2] changing his surname by deed poll to allow his forename to be incorporated into his title.

[4] According to Alistair Cooke, Baron Lexden, a Conservative member of the House of Lords, Nicholls had an affair with the Russian spy John Vassall.