The Irish National Teachers' Organisation has voted by 63% to 37% to accept the Croke Park pay deal for public servants.
The union's leaders have urged acceptance of the deal.
The INTO's decision comes after two of the main teaching unions voted to reject the proposals.
Speaking after his union accepted the deal, INTO Deputy General Secretary Noel Ward said 'It's our job now, both for those in favour in INTO and those who voted against it, to see that it is delivered.
'We believe that it is now likely to cross the line and be accepted but delivery is the issue now'.
Earlier two other teaching unions the ASTI and the TUI rejected the agreement.
The Teachers' Union of Ireland rejected the deal by a margin of three to one, while the Association of Secondary Teachers Ireland voted by a margin of 62% to 38% to reject the agreement.
TUI General Secretary Peter MacMenamin attributed the large margin to the open-ended demand for the renegotiation of the teachers' contract, which some viewed as buying a 'pig in a poke'.
Asked whether the TUI would be bound by any overall decision in favour of the deal by public sector unions, Mr MacMenamin said that would be decided after the final result was known.
However, in the past he has not ruled out a go it alone position by the TUI.
The executive committee of the TUI will consider the result at a meeting today and will vote according to the ballot result at the forthcoming meeting of the Public Services Committee of Irish Congress of Trade Unions.
ASTI General Secretary John White said: 'Clearly the ballot results of the second-level teacher unions indicate that a one-size fits all agreement is not appropriate for second level.
'Second-level teachers have been put to the pin of their collars dealing with all the difficulties of society which manifest in their classrooms at a time when resources have been cut and the whole middle management structure has been removed from schools.'
Taoiseach Brian Cowen described the decisions of the TUI and the ASTI as 'disappointing'.