First Minister Rhodri Morgan has announced he will stand down as leader in the middle of the Welsh assembly's next term.
He will lead Labour into the election in 2007, but it was the "absolutely logical answer" to step down in 2009 if the party was successful.
Mr Morgan, 65, has been first minister since succeeding Alun Michael in 2000.
He said he was "as fit as a flea" and had an "undiminished appetite for the business of government".
Mr Morgan had to tell the Labour party now whether he wanted to stand again.
RHODRI MORGAN FACTFILE
Born Cardiff 29 September 1939
Graduate of Oxford and Harvard Universitities
Cardiff West MP 1987-2001
Cardiff West AM 1999-
Economic Development Minister 1999-2000
Married to Cardiff North MP Julie Morgan; one son, two daughters
The former Cardiff West MP was elected as an AM when the assembly was established in 1999.
In a statement, Mr Morgan said he intended to lead the party into the next election and seek re-nomination in his constituency.
"This is a decision to which I have given very careful consideration," he said.
"I am lucky to continue in good health and with an undiminished appetite for the business of government.
"The schedule which faces any first minister is highly demanding. It takes up seven days in most weeks and it is never without its list of challenges.
"On this, the final day of another busy and exacting assembly term, my decision to seek to continue in office is motivated by the wish to see a set of key issues for Wales through to a successful conclusion."
'I feel fit as a flea, despite some minor niggles here and there' said Mr Morgan
Nick Bourne, the leader of the Welsh Conservatives in the Welsh assembly, said "four more years of Rhodri Morgan's mismanagement will be a disaster for Wales".
"Time and again, Rhodri Morgan has been found wanting. His period in office has been marked by an inability to take the tough decisions needed to improve life for the people of Wales."
Plaid Cymru leader Ieuan Wyn Jones claimed that Rhodri Morgan had been forced to show his hand by "internal pressures in his group".
Mr Jones said the electorate in 2007 would face a clear choice "of a rudderless Labour group, with Jane Davidson, Andrew Davies and Carwyn Jones squabbling for succession, or a Plaid Cymru..government that can actually deliver on the matters that really affect everyday life in Wales".
Asked about a possible successor, Mr Morgan said: "I think it's much too early to talk about that.
"I don't think there would be a shortage of candidates with the required maturity, political skill and so on. I will not be proposing to give a papal blessing to a successor."