The ancestral lands of Pitcairn lie in the Scottish Parish of Leslie in Fife, and are reputed to be one of the oldest of the ancient Kingdom of Scotland.Major (John) Pitcairn (1722-1775), father of Midshipman Robert Pitcairn, was an officer from Fife, Scotland born at Dysart, the son of the Rev. David Pitcairn and his wife, Katherine Hamilton. John Pitcairn was baptised at Saint Serf's Church in the then flourishing merchant port of Dysart, on December 28, 1722.
John Pitcairn married Elizabeth, daughter of Robert Dalrymple, of Arnsfield, Dumfriesshire, and Dreghorn Castle, in Midlothian. Elizabeth (Betty) Dalrymple (1724-1809), was a distant cousin of his father's old Colonel, the Earl of Stair. They had 6 sons (one dying in childhood) and 4 daughters. Their eldest son, David, followed his uncle, Dr. William Pitcairn, to become an eminent physician at St. Bartholomew's Hospital in London. Robert became a midshipman, and in 1767 he was the first to sight Pitcairn Island. William and Thomas joined their father in the Marines. Alexander, the baby, born in Kent, was only 7 when John died; eventually he entered the English legal profession. The daughters, Annie, Katharine, Johanna and Janet, married naval or army officers of good family.
John Pitcairn was commissioned Lieutenant in Cornwall's 7th Marines in 1746. When the Marines were established permanently in 1755, he was confirmed in that rank. He was commissioned as a Captain on June 8, 1756 while serving aboard H.M.S. Lancaster, probably en route to Canada. Aged 48 he was promoted to Major, April 19, 1771, in the Chatham division. Some sources indicate that he was the Commander of the Marine detachment on Carteret's ship H.M.S. Swallow, but this has not been verified.