The Republic of Ireland's Green Party has agreed to join Prime Minister Bertie Ahern's Fianna Fail in forming a coalition government.
Bertie Ahern has led coalition governments since 1997
The party's membership voted overwhelmingly to back the deal, a day after it was struck with the party's six legislators.
The agreement will see the Greens in an Irish government for the first time.
The deal means it is now likely that Mr Ahern will be re-elected taoiseach when the parliament convenes on Thursday.
The election on 24 May returned Mr Ahern but without a clear majority.
Fianna Fail won 78 of the country's 166 parliamentary seats last month, but Mr Ahern's coalition partners the Progressive Democrats saw their tally drop from eight to two.
So Mr Ahern needs the Greens to give him the margin he needs.
The backing of the Greens' six legislators was secured after nine days of tough negotiations.
Concessions from Fianna Fail on environmental and transportation policy finally secured their support.
Fianna Fail won 78 seats in the 166-seat assembly, but a decline in the vote of its previous coalition partners, the Progressive Democrats, forced Mr Ahern to look for more new allies.
Fianna Fail made policy concessions to win the Greens
Besides the Greens, Mr Ahern can count on several independents and two surviving Progressive Democrats.
The main opposition Fine Gael polled well, winning 51 seats, but its potential coalition partner Labour fared less well.
Even if the Greens had instead agreed to join Fine Gael and Labour, the three parties combined could not have overtaken Fianna Fail and the PDs.
The Republic of Ireland's system of proportional representation means that parties' representation in the Dail (lower house of parliament) closely matches their percentage of the vote.
Bertie Ahern has led a coalition government since 1997 - a period of sustained economic growth for the Republic.