Gregory, George (1790–1853), physician and vaccinator, was born on 16 August 1790 in the precincts of Canterbury Cathedral, second son of the Revd William Gregory, one of the six preachers there, and his wife, Catharine Sayer. Gregory received his early education at the King's School in the city. On the death of his father in 1803 he moved to Edinburgh to live with his paternal uncle James Gregory, professor of medicine at the university medical school. He studied arts at Edinburgh University before following in the footsteps of his uncle and his grandfather John Gregory by studying medicine. Gregory received the best possible education of the day. From 1806 he attended courses at the Edinburgh medical school. In 1809 he moved to London where his studies were supervised by Matthew Baillie, the distinguished anatomist and a close friend of James Gregory. There Gregory attended lectures in anatomy by Benjamin Brodie at the Windmill Street School and in chemistry by William Brande. In 1811 he returned to Edinburgh and obtained his MD with a thesis on pulmonary tuberculosis. In 1812 Gregory became a member of the Royal College of Surgeons and entered the Army Medical Service. The following year he was sent to the Mediterranean. In 1816 he returned to London, became a member of the Royal College of Physicians, and set up in practice. From 1817 he served as physician and later consulting physician to the St George's and St James's Dispensary.

Gregory's reputation among his contemporaries rested on his teaching and textbooks. From 1818 he gave a course of lectures on the practice of medicine at the Windmill Street School, which he published as Elements of the Theory and Practice of Physic (1820). The structure of the text was traditional, drawing on the works of William Cullen, the great Scottish practitioner, but it incorporated much new material on recently identified diseases, the novel ideas of the French pathological anatomists, and the tissue theory of Xavier Bichat. The work was widely praised and it went through several editions in Britain and the United States. In 1842 Gregory was appointed lecturer in skin diseases at St Thomas's Hospital and again produced a textbook. His Lectures on the Eruptive Fevers (1843), describing the character and treatment of the most common exanthemata, particularly smallpox, was less well received. Gregory was applauded for the clarity and directness of his lectures, but his abrupt manner served him less well in his practice.

Gregory also published a large amount of original material, much of it on smallpox and vaccination—as physician to the Smallpox and Vaccination Hospital, a post he held from 1824 until his death, he had access to a unique amount of clinical material. His most significant and controversial finding, published in Observations on Vaccination and Smallpox (1841), was that the severity of smallpox suffered by previously vaccinated patients bore no relationship to the degree of scarring left by the original vaccination. At the time most practitioners believed that levels of immunity were reflected in the size and form of the vaccine cicatrix. Gregory served on the Provincial Medical and Surgical Association's vaccination committee, investigating the permanence of immunity conferred by the procedure, though he disagreed publicly with the final report penned by its chairman, John Baron. He also joined the debate on the relationship of cowpox—the complaint from which vaccine was derived—to smallpox and related diseases. Gregory was a prolific contributor to medical journals: one biographer reported that he had produced no fewer than 212 papers.

Gregory was an active member of the profession. In addition to holding membership in the Provincial Medical and Surgical Association, he was a founder member of the Westminster Medical Society and in 1821 he became a fellow of the Medico-Chirurgical Society. In 1839 he was made a fellow of the Royal College of Physicians and he was also a fellow of the Royal Society. In late 1851 Gregory began to display symptoms of heart disease. He died at his home at 6 Camden Square, London, on 25 January 1853, and was buried in Kensal Green cemetery.