John Calef was a doctor and British loyalist who served on the side of the crown during the Revolutionary War. Calef was born in Ipswich, Massachusetts, on August 30, 1725, to Robert Calef and Margaret Staniford. Calef first married Margaret Rogers of Ipswich, who died in 1751; they had two children. After Margaret's death, Calef married Dorothy Jewett of Rowley, Massachusetts, in 1753; together they had fifteen children.
John Calef studied medicine at the Boston Latin School and became a naval surgeon in 1745. He served at Fort Halifax, now the town Winslow, Maine, for two months in 1755 and in 1756, started five years of service under Colonel Ichabod Plaisted and Generals Lord Loudoun and Jeffery Amherst. In 1764, Calef was elected to the General Court of Massachusetts but, remaining loyal to the King during the Revolutionary War, was forced to leave the position in 1779. He and his family fled to St. Andrews, New Brunswick, in the Penobscot region (Maine) and was the surgeon at Fort George (Castine, Maine) during a 21-day siege in July and August 1779. Calef traveled to England in 1780, to lobby the creation of a new province to be called New Ireland, but was unsuccessful. While in England, he published The Siege of Penobscot, his account of the conflict.
In 1784, Calef and his family fled to a loyalist community in St. John, New Brunswick, where he was the only qualified doctor. He was appointed surgeon to the British garrison at Fort Howe and served there until 1800, though in 1791 he moved his family to a house in St. Andrews. He joined his family permanently in St. Andrews and lived there until his death in 1812.