Over 65% of those who voted accepted the agreement.
SIPTU President Jack O'Connor said SIPTU's members in the public service have decided to go with a medium term strategy which protects their interests in the matters of pay, job security and pensions while providing a framework for the reinstatement of agreed rates over time.
He said the onus would now pass to those at the top of society who have contributed little or nothing to the resolution of the country's economic problems while working people and those who depend most on public services had carried the lion's share of the burden.
The Croke Park agreement is now set to be ratified by the Public Services Committee of Congress on Tuesday.
Earlier, the deal received a major boost after another of the biggest unions, IMPACT, voted to accept it.
77% of IMPACT's 60,000 members voted in favour, with 23% against.
Focus will now shift to implementation of the agreement, and the securing of cost savings through enhanced productivity and efficiency measures.
The agreement guarantees no further pay cuts or compulsory redundancies for four years in return for productivity concessions by over 250,000 Government employees.
However, a number of issues remain and some unions who rejected the deal have said they may not abide by the overall Congress majority vote.
Practical difficulties may emerge in individual workplaces when management in the various sectors start implementing reforms, including redeployment of staff and new rosters.
It is also unclear how long it will take for reforms to deliver quantifiable savings.
Some of those savings, if any, are due to be returned to staff, particularly the lower paid, in a review next spring.
It has also not yet been agreed how those savings will be distributed between staff in different sectors, given that some may face greater demands for change than others.
