 All male Upper Canadians between 18 and 60 years of age were members of the Sedentary Militia, which was called into active duty during the Rebellions of 1837.Macdonald served as a private in the militia, patrolling the area around Kingston, but the town saw no real action and Macdonald was not called upon to fire on the enemy.Although most of the trials resulting from the Upper Canada Rebellion took place in Toronto, Macdonald represented one of the defendants in the one trial to take place in Kingston.