Leslie, whose family came originally from Aberdeenshire, was a descendant of the ‘fighting bishop’, John Leslie of Clogher.
A leading Orangeman, who joined the committee of the Grand Orange Lodge in September 1824, Leslie was encouraged then and in the autumn of 1825, when a dissolution was expected, to stand again for Monaghan, with Protestant and Tory support. Reported to be ‘more fond of money than ever’, so that he apparently would ‘not spend a stiver upon elections’, he was advised to avoid a contest by allying with the new interest of Evelyn Shirley*, hitherto an absentee landlord, who ostensibly favoured Catholic relief.
Lucky to escape without injury during the ugly scenes which greeted his arrival on the hustings, Leslie was forced to resign on the sixth day of the poll. His defeat, largely owing to the spirited opposition of the Catholic freeholders, was one of the spectacular reverses suffered by the Protestant interest at the general election of 1826.
It was at first asserted that Leslie would offer again for Monaghan at the general election of 1830, but he ruled himself out as sick. He apparently thought his position was too weak to risk another rebuff and gave his interest to the like-minded Lord Blayney’s son, who was returned with the now ministerialist Shirley, a result which was thought likely to strengthen his future interest.
