John Gairdner MD FRCS (1790–1876) was a Scottish physician.
He was the eldest son of Captain Robert Gairdner of the Bengal artillery, and brother of William Gairdner, born at Mount Charles, near Ayr, on 18 September 1790. When he was five years old his father was killed by the kick of a horse. He received his school education at Ayr academy, but the family moved to Edinburgh in 1808, and there he took his degree of M.D. in 1811. He spent the winter of 1812 in London, studying anatomy under Charles Bell. 
In 1813 Gairdner went into practice in Edinburgh in partnership with Dr. Farquharson. In the same year he became a fellow of the College of Surgeons of Edinburgh, and four years later began to act as examiner for them; for many years the College's treasurer, he was president from 1830 to 1832. This appointment gave him a seat in the unreformed town council of Edinburgh. The election for the parliament of 1831 was entirely in the hands of the town council, and Gairdner, a reformer, seconded the nomination of Francis Jeffrey, Lord Advocate. The majority of the council, however, disregarded a petition presented to them and elected Robert Adam Dundas. They departed through back streets, while a mob attacked the Lord Provost and threatened to throw him over the North Bridge.
With his friend William Wood, Gairdner supported a move allowing medical students for the degree at Edinburgh University the right to receive some professional training from extra-academical lectures. He also gave evidence before parliamentary committees in London, on behalf of the Edinburgh College of Surgeons, in the efforts made to secure a legal status for licensed practitioners of medicine and surgery extending throughout the UK, ahead of the Medical Act 1859.
Gairdner joined a small group of Unitarians, and this was thought to have hampered his career. He was involved in setting up of a new unitarian chapel in Edinburgh; but later returned to the Church of Scotland.
Gairnder died on 12 December 1876, at the age of 86.
Gairdner wrote in Transactions of the Medico-Chirurgical Society of Edinburgh, and in the medical journals, almost to the end of his life. He also published two lectures, one on the history of the Edinburgh College of Surgeons, the other on the early history of the medical profession in Edinburgh. He published in his later years a Calendar printed on cardboard, with a cardboard slide, for the verification of dates.
Gairdner married in 1817 his cousin Susanna Tennant, a granddaughter of Dr. William Dalrymple of Ayr, whom he survived by 16 years. He was survived by three sons and two daughters. William Tennant Gairdner was the eldest son, and James Gairdner the second.
- Stephen, Leslie, ed. (1889). "Gairdner, John". Dictionary of National Biography. 20. London: Smith, Elder & Co.
- O'Neill, Tim. "Gairdner, William Tennant". Oxford Dictionary of National Biography (online ed.). Oxford University Press. doi:10.1093/ref:odnb/33308. (Subscription or UK public library membership required.)
- Loades, David. "Gairdner, James". Oxford Dictionary of National Biography (online ed.). Oxford University Press. doi:10.1093/ref:odnb/33307. (Subscription or UK public library membership required.)