The ASTI has voted to sign up to the Haddington Road pay deal.
Some 57% of the union’s 17,000 members voted to accept the deal, in the third ballot held by the secondary teachers' union.
The move now means that every public sector union has signed up to the deal, which aims to cut the public pay bill by €1bn by 2015.
The vote also ends the threat of strikes and possible school closures in the New Year.
Members of the Association of Secondary Teachers of Ireland (Asti) had refused to work outside normal hours, including meeting parents before or after school, in a long-running dispute over the Haddington Road Agreement.
Asti general secretary Pat King said it had secured a number of commitments that the Government had to live up to in a specified timeframe.
“The Asti has informed the Department of Education and Skills that any failure by the Government to meet its commitments under the Haddington Road Agreement, including any delay in the implementation of those commitments, would be unacceptable to the Asti and would be met with strong action from the union,” he said.
Asti claimed the deal includes commitments to address the high number of teachers on short-term or part-time contracts, establishment of a working group to look at concern about junior cycle reform and a new agreement on best use of the Croke Park hours.
Education Minister Ruairi Quinn said he welcomed the outcome.