Political reaction:Taoiseach Bertie Ahern led tributes to retiring Labour leader Pat Rabbitte, describing him as a "politician to be reckoned with".
Mr Rabbitte's "capacity and wit had enlivened public debate over many years" and he was "one of the most eloquent and effective parliamentarians in the House", said Mr Ahern.
"His genuine passion for his cause was married to a forensic intelligence and considerable wit that made him a politician to be reckoned with, as well as a parliamentarian who engaged the public's interest", he said.
Fine Gael leader Enda Kenny said it had been an "honour" to work closely with Mr Rabbitte since the pair signed up to the Mullingar Accord, a pre-election alliance between their two parties. "At a time when we need a better and broader vision for our country we have lost one of the few political leaders who espoused, passionately, such a vision," said Mr Kenny.
"I thanked him for his work in respect of our country over the last five years and in particular his and the Labour Party's decision to give the Irish people a real choice in the recent general election."
Green Party leader and Minister for the Environment John Gormley described Mr Rabbitte as "an extremely competent and witty parliamentary performer".
"He managed to both entertain and enliven the Dáil over the last five years," he said.
Wexford TD Brendan Howlin, who contested the leadership of the Labour Party in 2002, said he had been "surprised" by the decision which Mr Rabbitte conveyed to him in a phone call yesterday morning. I had discussions with Pat in the immediate aftermath of the election. I certainly discerned that he was not going to consider his position in the short term.
" He was talking in terms of preparing the party for the local elections. I was of the view that any decision he made would have been at the end of his mandate," he said. Mr Howlin said Mr Rabbitte was a "consummate politician" and "a tremendously effective parliamentarian - probably one of the best we've seen in the last 20 to 30 years".
He said Mr Rabbitte had suffered in the general election as party leader having to take on Bertie Ahern which had been like "nailing quicksilver".
"In truth the confluence of events in 1992 [ when Labour gained 15 seats] made things profoundly different for [then leader] Dick Spring. It's much more difficult to attack a government led by Bertie Ahern."
Sinn Féin's Dáil leader Caoimhghin Ó Caoláin wished Mr Rabbitte well on the backbenches. "Though we have our political differences and have had an occasional spat on the floor of the Dáil chamber, I would like to wish Pat Rabbitte well in his continuing role as an elected member of the Dáil," he said.
SDLP leader Mark Durkan described Mr Rabbitte as "an articulate parliamentarian and a compassionate politician".
Siptu general secretary Joe O'Flynn said Mr Rabbitte, who is a former ITGWU group secretary, had "championed a fairer society and in particular workers' rights. "He had an intimate knowledge of the world of work and how progressive political policies could advance the interests and standard of living for ordinary people," he said.
