John Alexander Mathieson (May 19, 1863 – January 7, 1947) was a politician and jurist of Prince Edward Island, Canada, and the 12th premier.

The Lieutenant-Governor of Prince Edward Island asked Mathieson as leader of the opposition to form a government, which he did, going on to win a mandate in the 1912 general election.

The province was also at risk of losing representation in the House of Commons of Canada due to population shifts.

Mathieson persuaded the federal government to agree to an amendment to the British North America Act guaranteeing the province a minimum of four MPs in perpetuity.

In 1917, Premier Mathieson left politics to accept an appointment as Chief Justice and served in that position until he retired in 1943.