He was the MLA for Argenteuil in the Legislative Assembly of Quebec from 1897 to 1910, held several ministries, and helped rewrite several provincial Codes.

His brother, Robert Stanley Weir, would become famous as a judge and author of the English verses for O Canada.

During the time he practised law, Weir also wrote for The Montreal Star from 1880–1881 and the Argenteuil County News from 1895–1897.

In 1897, he ran again and succeeded in winning the riding of Argenteuil, representing the Liberal Party of Quebec.

Upon appointment as a judge for the Quebec Superior Court on January 11, 1910, Weir resigned his seat.