Sara Jeannette Duncan was born in Brantford, Ontario, in 1861. She attended the Toronto Normal School, then left teaching for a career in journalism. She worked as an editorial writer and book reviewer for the Washington Post, then wrote for the Toronto Globe under the name of “Garth Grafton,” and contributed a column to whose founder was Goldwin Smith. She was also parliamentary correspondent in Ottawa for the Montreal Star.
In 1888 Duncan set off on a round-the-world trip as correspondent for the New York World and the Montreal Star. In Calcutta she met her future husband, Everard Cotes, an Englishman serving there as curator of the Indian Museum. They married two years later. Duncan lived in India for twenty-five years, with extended stays abroad in London and frequent trips to Canada.
A prolific and popular writer of fiction, Duncan set nearly half of her novels in India. The Imperialist (1904), generally considered her finest, is her only novel set in Canada. During and after World War One she devoted much of her time to playwrighting.
In 1922 Duncan and her husband retired to England.
Sara Jeannette Duncan died in Ashtead, Surrey, England in 1922.