Paul Elliott, a teacher from Fort Frances, will be taking over from president Ken Coran starting July 1.
Members of the Ontario Secondary School Teachers' Federation elected Elliott at their annual meeting Sunday in Toronto.
Coran had decided not to run for re-election.
The union, which represents about 60,000 teachers and education workers, has been battling the Ontario Liberals for the past year.
The fight reached a boiling point in January when the government imposed new two-year contracts that cut benefits and froze the wages of most teachers.
The union recently recommended that teachers resume extracurricular activities, but Coran warned that many may not go back.