Mathew was returned for the county after a contest in 1790, unseated in favour of John Bagwell I, but re-elected in 1796. He opposed the Union, to his father’s distress, as it damaged expectations of a marquessate, to redeem which he promoted a loyal address from the county and brought in two loyalist Members. Failing to achieve his aim through Cornwallis, Lord Landaff, who did become a representative peer, subsequently applied to Lord Hardwicke in May 1801 and August 1802, but nothing came of it, perhaps because his son was reckoned in opposition at Westminster.
In the spring of 1804 it was noted that Mathew was raising a regiment, had been well disposed to the Ponsonbys, but would probably support government. He had been among the Prince of Wales’s parliamentary recruits from Ireland in February 1804.
