Members of Fórsa, SIPTU and the ASTI have voted to accept the new public sector pay deal.
Fórsa, the country's largest public service trade union, backed the agreement by a majority of 91%.
90% of SIPTU members who cast ballots voted in favour while the ASTI ballot recorded an acceptance rate of 83%.
It means the pay agreement looks certain to pass on an overall basis when it is formally ratified tomorrow.
In August, the Government reached agreement with unions and staff associations on a set of proposals that would see public sector workers receive a 6.5% pay increase over two years.
The deal would deliver increases of 3% backdated from 2 February 2022, 2% from 1 March 2023 and 1.5% or €750, whichever is the greater, from 1 October 2023.
This would come on top of a 2% increase already included in the existing public sector pay agreement, 'Building Momentum'.
After agreement was reached, the Irish Congress of Trade Unions (ICTU) said that individual unions should ballot their members on whether to accept or reject the deal.
Yesterday, the Irish Nurses and Midwives' Organisation (INMO) voted in favour of the deal and last week so too did the Irish National Teachers' Organisation (INTO) and the Teachers' Union of Ireland (TUI).
Announcing Fórsa's result today, the union's General Secretary Kevin Callinan said it was a strong statement of support for the pay deal.
"These pay terms emerged from a review process necessitated by the surge in inflation and the ongoing cost of living crisis," Mr Callinan said.
"In the medium term we do expect to be back in negotiations next year to secure pay terms beyond the lifetime of the current agreement," he added.
SIPTU Deputy General Secretary, John King said the agreement represented a significant improvement in pay for public service workers.
"It will help to offset the cost of living and inflation crisis and will also provide long lasting improvements to the terms and conditions of SIPTU members in the public service," he said.
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The ballot results will be aggregated at a meeting of the ICTU Public Services Committee tomorrow, but it is expected the agreement will be passed on an overall basis.
Tánaiste Leo Varadkar said he was "very happy" about this.
"First of all, it gives public servants a well-deserved pay increase. Our teachers, our gardaí, our doctors, our local authority workers, our civil servants and also it gives us industrial peace," Mr Varadkar said.
"We know all our public services will operate well into next year without the risk of any strike action and that's a real positive," he added.
Minister for Public Expenditure and Reform Michael McGrath welcomed the acceptance of the pay agreement.
"I very much welcome this deal which will bring significant benefits and ease the pressure on about 400,000 public servants and about 200,000 public service pensioners and gives us certainty, which is really valuable at a time of uncertainty around the world," Mr McGrath said.
"It would normally be the case that some months before the end of a deal that there would be negotiations on a possible successor agreement, so I anticipate the same practice would be followed in the later part of next year," he added.