Lord Abercorn intended to put Hamilton up as a candidate for County Donegal as soon as he could obtain sufficient interest there, or else for County Tyrone.[3] The death of Abercorn's personal agent, James Hamilton, in 1806, damaged his personal interest in Donegal, and Viscount Hamilton was obliged to retire before the contest.[5] Instead, he was put in (while underage) for Dungannon by Abercorn's political ally, Thomas Knox, 1st Viscount Northland, at a by-election in January 1807.[3] At the 1807 general election, in May, Abercorn declined a compromise with Earl Conyngham to put Hamilton in at Donegal, and he was instead returned, still underage, for Liskeard, by his half-cousin Lord Eliot.[3]
He evidently suffered from chronic illness, as his father described him as "long dying" in declining an offer from Lord Eliot to return him for Liskeard again in 1812, although he was a founding member of Grillion's that year.[3] He died in his house in Upper Brook Street on 27 May 1814. His eldest son, James, would succeed his grandfather as Marquess of Abercorn four years later. His widow Harriet would in 1815 marry her brother-in-law, the 4th Earl of Aberdeen,[1] with whom she had another 5 children.