Theophilus Mack immigrated to Canada in 1832 with his parents. His father had been a minister of the Church of England. Mack was one of the first pupils of Upper Canada College.
During the rebellion of 1837-38, he was a lieutenant in the Provincial Navy.
Mack studied medicine in the Military Hospital at Amherstburg, graduating at Geneva College, New York in 1843. He obtained his provincial license in 1844 and settled in St. Catharines. He practiced medicine in St. Catharines and served as a professor of Materia Medica at the Buffalo Medical College.
Mack developed the St. Catharines mineral waters by founding Springbank as a thermal establishment consisting of a hotel and sanatorium in 1850. Mack was the first doctor in Canada West to specialize in the treatment of women’s’ diseases. He was instrumental in establishing “The St. Catharines General and Marine Hospital” in 1865. In 1873-74, he established the first “St. Catharines Training School and Nurses’ Home” using the Florence Nightingale system.