Tassie was born on 10 March 1815 in Dublin, Ireland. He was the third child of Mary (née Stewart) and James Tassie. He had seven brothers and sisters. In 1834 Tassie and his wife moved with the rest of his family to Nelson Township in Upper Canada. In 1856 he was awarded a Bachelors of Arts from the University of Toronto, and in 1858 he received a Master of Arts from the same institution.
