Born in Peterhead, William Seller was the son of a merchant who died at an early age. His mother, with her three children, came to Edinburgh where Seller was educated at the High School. At Edinburgh University he took a course in Classics and Philosophy before studying medicine, graduating with an MD in 1821. Shortly after graduation, he opened a boarding house for medical students and held classes of preparation for examinations. He was appointed a physician to the Royal Infirmary and to the Royal Public Dispensary. On being elected a Fellow of the College he became a lecturer on materia medica in the Extra-mural School. Seller was the writer of valued reviews and essays in medical journals which he edited such as 'Homeopathy, the last popular delusions' in the 'Northern Journal of Medicine'; 'The Character of Medicine as an Art' and 'Some of the Metaphysical Aspects of Physiology' in the 'Edinburgh Medical Journal', of which he was joint-editor for many years.