By-elections to the 12th Canadian Parliament were held to elect members of the House of Commons of Canada between the 1911 federal election and the 1917 federal election. The Conservative Party of Canada led a majority government for the 12th Canadian Parliament.
The list includes Ministerial by-elections which occurred due to the requirement that Members of Parliament recontest their seats upon being appointed to Cabinet. These by-elections were almost always uncontested. This requirement was abolished in 1931.