Early in 1854 Lawson entered the army as an assistant surgeon, and in March of that year he left England with the first draft of troops for Malta.

Although he had been gazetted assistant surgeon to the third battalion of the rifle brigade he was invalided home and at the end of the war he resigned his commission.

in 1857, he settled at 63 Park Street, Grosvenor Square, and turned his attention more especially to ophthalmic surgery, probably at the suggestion of Sir William Bowman, who had been assistant surgeon at King's College Hospital whilst Lawson acted as house surgeon.

He served as a member of the council of the College of Surgeons from 1884 to 1892, and in 1886 was appointed surgeon-oculist to Queen Victoria.

He married, on 5 March 1863, Mary, daughter of William Thomson, of the Indian medical service, by whom he had seven sons.