John Thomas Haig (December 15, 1877-October 23, 1962) was a Manitoba politician. He served as parliamentary leader of the Manitoba Conservatives from 1920 to 1922.

Born in Colborne, Ontario, Haig received his B.A. from Manitoba University and worked as a Barrister-at-law. He was elected to the Winnipeg Public School Board in 1908, and continued to hold this position after entering provincial politics.

Haig was first elected to the Manitoba legislature for Assiniboia in 1914. He was soundly defeated in the Liberal landslide of 1915, but returned to the legislature in 1920 at the head of the Conservative Party list in Winnipeg (Winnipeg elections were determined by a form of proportional representation at this time).

Conservative leader R.G. Willis was unable to win a seat in the 1920 election, and Haig was called to lead the eight-member caucus in parliament. He ran for the party's official leadership in April 1922, but was defeated by Major Fawcett Taylor.

Haig was re-elected to the legislature in 1922, 1927 and 1932, and remained an important voice for the party. In August 1935 he was elevated to the Canadian Senate by Richard Bennett. From 1945 until 1957, Haig was Leader of the Opposition in the Senate for the Progressive Conservatives. After the 1957 Canadian election, Haig joined the Cabinet of John George Diefenbaker, serving as Minister without portfolio and Leader of the Government in the Senate until May 11 1958. He retired from the Senate on January 17 1962.