From his youth Campbell was intended for a parliamentary career, being mentioned as a possible candidate for Inverness-shire as early as December 1746; when he was 19.

Aware that Fraser's acquisition of a Highland regiment in January 1757 heightened his political credibility with Inverness-shire voters, Pryse refused to assist in the recruitment process; but it was his support for the Irish Cattle Importation Act during February and March 1759 that deeply damaged his relationship with his constituents.

By February 1761 Argyll had made it clear he would oppose reselection of Pryse for Inverness-shire, with the result that the latter, with the support of the Earl of Bute, stood for and won the Nairnshire seat.

[1] Despite being created a lord of treasury in August 1766 and being re-elected to parliament on 4 December 1766, Campbell was still faced the problem that under the Scottish electoral system Nairnshire would not be represented at the next election.

As a result, he switched to his Welsh interest and was elected for the Cardigan Boroughs on 24 March 1768, but died on 14 December of the same year.