Mr Ruairí Quinn has this afternoon announced his decision to step down as Labour Party leader.
In a statement Mr Quinn (56) said: "I have decided not to seek a second term as leader of the Labour Party when my current term expires. Accordingly I have written to the general secretary of the party informing him of my decision.
"I will complete my mandate as leader with a vigorous campaign during the forthcoming referendum on the enlargement of the European Union."
He said: "I have been honoured and proud to be the leader of the Labour Party, the oldest political party in Ireland and one which has given exceptional service and commitment to the people of Ireland and the Irish state".
Mr Quinn oversaw a Labour campaign that won 21 seats in the May general election - the same number it held in the last Dáil. It is understood Mr Quinn was disappointed the party had not gained extra seats.
"While the last general election may not have brought all the Labour Party would have wished, we did return the second largest parliamentary Labour Party in our history.
When asked his reasons for stepping down Mr Quinn said, "I could serve the party in other ways and that being party leader for another 6 years was not something that I wanted to do because I didn't feel that I could continue to do the job in the way that I had done it in the past."
The party is due to ask its membership to elect a new leader before October 25th in a new approach to deciding the role. The winner of the October leadership race will be given a six-year term.
There is no obvious successor to Mr Quinn. But the deputy leader, Mr Brendan Howlin, will face competition from Ms Joan Burton and former Democratic Left member Mr Eamon Gilmore.
However, the unpredictability of the new procedure for electing the next leader means that some less high profile candidates such as Limerick's Ms Jan O'Sullivan may also enter the race.