In 1760 Campbell was returned unopposed for Lanarkshire on the united interest of the Dukes of Douglas and Hamilton, with the support of the Duke of Argyll and Robert Dundas of Arniston.
Argyll’s death, followed by that of the Duke of Douglas, left Campbell without a patron. In December 1761 the dowager Duchess of Douglas recommended him to Bute as ‘ready to oblige your Lordship’.
As early as August 1766 Campbell opened his campaign for the 1768 general election.
At the general election of 1774 Campbell stood once more for Lanarkshire, regarded by the Argyll-Hamilton family as a dangerous opponent to Andrew Stuart. On 27 July 1773 William Mure warned the Duchess:
Shawfield I hear is in play, I wish the Duke [Argyll] could throw an invitation in his way, to return by Inverary that you might have a conference with him. He is a great card as they are now shuffled.
The Duchess replied, 1 Aug.:
What shall I say to Shawfield if he comes this way. I think the boroughs [Lanark, Linlithgow, etc.] might be offered to him. He was once too high and mighty to accept of such an offer and he may be so yet, but if they could keep him out of the county, I think it would be worthwhile.
Another compromise (rejected by Andrew Stuart as prejudicial to the Hamilton interest) proposed that Campbell should be adopted for the county and in return should pay Stuart’s expenses for the Burghs, ‘whatever sum that might amount to’.
He died 12 May 1777.
