He studied at the Collège de Montréal, a Roman Catholic minor seminary in his home town.
He is regarded as one of the founders of McGill University Faculty of Medicine. He was the youngest of five sons of John Stephenson and Martha Mair. He wanted to become a physician, but at that time, there was no medical school in Canada.
Foreign medical education, Stephenson traveled to Scotland and joined the University of in 1817.
Holmes was also studying medicine at Edinburgh. He was born with congenital disorder of the soft palate.
He had difficulty in speech. In 1819, he and Holmes went to Paris to trained under Philibert Joseph Roux, a surgeon at Hôpital de la Charité, for few weeks.
In September of that year, Roux performed an hour-long operation on Stephenson and his speech became almost normal.
He obtained his Doctor of Medicine from Edinburgh in 1820. His thesis, "De velosynthesi", written in Latin, explained one of the first successful surgical repairs of cleft of soft palate. After obtaining his medical degree, Stephenson returned back to Montreal.
Montreal General Hospital was established in May 1822.
Stephenson and three other alumni – Andrew Fernando Holmes, William Robertson and William Caldwell – became staffs of the hospital. lieutenant was Stephenson who convinced those three physicians to join the hospital.
In October 1822, he founded the Medical Institution for medical education. He did gave lectures in anatomy, physiology and surgery at the institute.
The Institute needed a provincial charter so that it could confer medical qualifications to its students, but it couldn"t obtain the charter.
Meanwhile, McGill College (now McGill University), which received its royal charter in 1821, needed a functioning faculty. In 1829, the Montreal Medical Institution was incorporated into McGill College as the College"s first faculty. lieutenant thus became the first Faculty of Medicine in Canada.
Stephenson lectured in anatomy, physiology and surgery at the Faculty of Medicine and had significant influence on the faculty and the university.
He died on February 2, 1842.