John Mortimer Courtney was born on July 22, 1838, in Penzance, England.

He was a Canadian civil servant. Privately educated in Penzance, he developed an interest in banking and, like so many of his generation, he took his ambitions to the colonies. He ventured first to India with the Agra Bank and then to Australia. In 1869, at the invitation of the Canadian minister of finance John Rose, he came to Canada and joined the Public Service of Canada working under John Langton as a chief clerk and assistant secretary to the Treasury Board. In 1878, he was promoted to deputy minister and ex officio deputy receiver general and secretary to the Treasury Board. For several years Courtney was a managing director of the Civil Service Building and Savings Society, and the zeal he showed in his profession extended into various philanthropic interests, among them the Associated Charities of Ottawa and the Canadian Patriotic Fund. In 1898, he was appointed Companion of the Order of St. Michael and St. George (CMG) and Companion of the Imperial Service Order in 1903. He retired in 1906.

In 1870, he married Mary Elizabeth Sophia Taylor (1845–1932). He died on October 8, 1920, in Ottawa, Ontario.