Campbell’s elder brother, who was interested in sitting for Glasgow Burghs in 1789, perished at Martinique in 1794. He himself was taken prisoner at Toulon. On becoming laird of Blythswood, he gave up the army.
Although his opponent was an acknowledged supporter of the Grenville ministry and they felt doubtful about him, there is no evidence of Campbell’s opposing them; but there was certainly bad blood between him and Alexander over the latter’s conduct of his unsuccessful petition, which led to such difficulties in local affairs that in August 1808 Robert Saunders Dundas was called in and contrived to make an uneasy peace between them.
Still in competition with Boyd Alexander for Renfrewshire, Campbell refused to come to terms with him before the election of 1812, even when Alexander offered to make way for him and thus unite the friends of government against the Whig sitting Member, claiming, though Campbell denied it, that he was thereby bound to support Alexander at the next election. He contested Glasgow Burghs instead. Despite a new agreement with Houstoun, his prospects were foredoomed and he again refused a last minute offer by Alexander to compromise in the county, in which he abstained from acting. In 1816 Alexander made another unsuccessful bid to come to terms with him over Renfrewshire, Campbell again refusing the option of contesting the county. Alexander concluded that Campbell had never forgiven him his conduct in 1806, despite the truce of 1808, and that he might even go to the length of joining his opponent to keep Alexander out of the county seat.
In 1818 Campbell, who was obliged to cede Glasgow to Houstoun by their agreement, was found a seat for Perth Burghs, where Melville procured him the interest of Sir David Wedderburn. His return cost him £1,500, more than twice as much as he was led to expect, and he soon wearied of his new constituents.