Sir Robert Walpole said that ‘of all the men he ever knew’, Lord Polwarth and his twin brother, Hume Campbell,
were the most abandoned in their professions to him on their coming into the world: he was hindered from accepting their services by the present Duke of Argyll [then Lord Ilay] of whose faction they were not.
On this the whole family went into opposition, with the result that its head, the 2nd Earl of Marchmont, was dismissed from his office of lord clerk register in 1733.
several young Members, who never spoke before, distinguished themselves ... as Mr. William Pitt, Mr. Lyttelton, Lord Polwarth and Mr. Hume, Lord Marchmont’s sons ... all for the bill.
On 16 Feb. 1737 Polwarth spoke against the bill imposing penalties on Edinburgh for the Porteous riots. Two days later he attacked Walpole for his ‘base treatment of his father’, to which Walpole replied that the reason why Lord Marchmont and his friends ‘were turned out was that they were endeavouring to be at the head of affairs’, and that a minister who put up with such behaviour ‘would be a pitiful minister’.
He died 10 Jan. 1794.
