The Leader of the Opposition in the Legislative Assembly of the Province of New Brunswick, Canada is a title traditionally held by the leader of the largest party not in government.

The Legislative Assembly of New Brunswick is the deliberative assembly of the New Brunswick Legislature, in the province of New Brunswick, Canada. The assembly's seat is located in Fredericton. It was established in Saint John de jure when the colony was created in 1784 but came into session only in 1786, following the first elections in late 1785. The legislative assembly was originally the lower house in a bicameral legislature. Its upper house counterpart, the Legislative Council of New Brunswick, was abolished in 1891. Its members are called "Members of the Legislative Assembly", commonly referred to as "MLAs".