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Military service

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 Captain George Well's Company of the Commercial Bank Guard.

Macdonald and the militia marched to Toronto to confront the rebels, and Sir Joseph Pope, Macdonald's private secretary, recalled Macdonald's account of his experience during the march:

"I carried my musket in '37", he was wont to say in after years. One day he gave me an account of a long march his company made, I forget from what place, but Toronto was the objective point: "The day was hot, my feet were blistered – I was but a weary boy – and I thought I should have dropped under the weight of the old flint musket which galled my shoulder. But I managed to keep up with my companion, a grim old soldier who seemed impervious to fatigue."

The Bank Guard served on active duty in Toronto guarding the Commercial Bank of the Midland District on King Street. The company was present at the Battle of Montgomery's Tavern and Macdonald recalled in an 1887 letter to Sir James Gowan that:

"I was in the Second or Third Company behind the cannon that opened out on Montgomery’s House. During the week of the rebellion I was the Commercial Bank Guard in the house on King Street, afterward the habitat of George Brown’s ' Globe '."

The Bank Guard was taken off active service on 17 December 1837, and returned to Kingston.

On 15 February 1838, Macdonald was appointed an Ensign in the 3rd (East) Regiment of Frontenac Militia but did not take up the position, serving briefly as a Private in the regiment, patrolling the area around Kingston. The town saw no real action during 1838 and Macdonald was not called upon to fire on the enemy, however the Frontenac Militia regiments were on active duty in Kingston while the Battle of the Windmill occurred.