SIPTU is to have a new general president on September 22nd, when Mr Jack O'Connor succeeds Mr Des Geraghty as leader of the country's largest union.
Mr O'Connor, who is 46 and currently the union's vice-president, had been widely tipped to take over from Mr Geraghty, who retires on reaching the age of 60.
The formal decision to appoint Mr O'Connor was taken by the union's executive council at a meeting following SIPTU's biennial conference in Galway.
Both he and the union's general secretary, Mr Joe O'Flynn, who is 45, are expected to lead the union for the next 15 years or so. A new vice-president will be elected to succeed Mr O'Connor, with Mr Brendan Hayes favourite to secure the post.
Mr O'Connor is taking over at a difficult time, with a number of factors putting pressure on the social partnership process, including conflict looming with the Minister for Transport, Mr Brennan, over his plans for Aer Rianta and CIÉ.
He acknowledged yesterday that Mr Geraghty cast "a long shadow" and would be difficult to replace.
In a tribute to Mr Geraghty at the conclusion of the four-day conference, Mr O'Connor described the outgoing president as an "eternal optimist" and drew laughter from delegates by adding: "In that regard we probably balance each other out."
The event, attended by 500 SIPTU activists and 100 guests and observers, concluded with a rendition of The Watchword of Labour, led by Mr Geraghty. At the conference dinner on Thursday night, he stressed that he was retiring from a job, but not from active participation in the trade union movement.
Tributes were paid to Mr Geraghty at the event by a number of people, including the Labour Party leader, Mr Pat Rabbitte, and the Irish Congress of Trade Unions general secretary, Mr David Begg.
The president-elect, Mr O'Connor, lives in Kildare and is married with three children.