On 15 June 1861, two months after the outbreak of the American Civil War, the 47th (Lancashire) Regiment of Foot, known as ‘Wolfe's Own’, set sail from the Irish port of Kingstown in the SS Golden Fleece for Canada. An invasion by the Federal forces seemed possible; Hamilton, Toronto, Kingston and Montreal were completely undefended. The Regiment reached Quebec on 2 July. Three days later it arrived, in steamers, at Montreal. Six companies were marched to temporary accommodation at Logan's Farm, four to St Helen's Island. By the end of August the Regiment was reunited in the Quebec Gate Barracks. Here, on 23 August 1861, Thomas James Macnamara was born. He was baptised eight days later by the Reverend Edward J. Rogers, a Presbyter of the United Church of England and Ireland and Chaplain to the Forces. Of Macnamara's mother, formerly Elizabeth Harvey, little is known. Thomas, his father, a Crimean veteran, now a Colour Sergeant, was an Irishman from County Clare.

The 47th Regiment remained in Canada until well after the Civil War was over, taking part in the repulse of the Fenian invasion in June 1866. Macnamara's earliest memory was of being on sentry-go at the age of five, with a toy rifle (the bayonet fixed) guarding Danny, his father's batman, who was asleep in the grass near the barracks' outer wall.