Published Saturday, 22 January 2011
Mr Cowen made the announcement in Dublin on Saturday following a week of unprecedented political turmoil.
He survived a motion of confidence over his leadership on Tuesday, but six ministers then resigned in the wake of the vote and his Cabinet reshuffle collapsed.
"At this crucial time the focus should be on politics rather than on the narrow focus of personality politics," he said.
"I'm concerned that renewed internal criticism of Fianna Fáil is deflecting attention from this important debate.
Taking everything into account after discussing the matter with my family I have taken, on my own counsel, the decision to step down.
Brian Cowen
"I want the party to be in the best possible position to fight that campaign as a united organisation fully supporting its leadership."
Mr Cowen, who will remain as Taoiseach until a successor is elected by the new Dáil after the General Election on 11 March, said he will now concentrate on Government business.
He said he has not spoken to senior party figures in relation to his decision, and that his resignation will not affect Government business.
On Friday, he seemed confident he could still lead the party into the poll and beyond, addressing reporters after a North-South ministerial meeting in Armagh.
Asked if he should now resign Mr Cowen said: "Of course not. I have the support of my party, as confirmed by democratic decision last Tuesday, to lead this party into this election and beyond.
"That is what I intend to do."
Addressing the Alliance Party's annual conference in Templepatrick on Saturday, leader of the main Opposition party Fine Gael, Enda Kenny, said the country is now the "laughing stock of Europe" over the past week's events.
"This is complete madness," Mr Kenny said. "We're now the laughing stock of Europe, we have a leaderless party and a powerless Taoiseach.
"It is a direct contradiction of what he said last week and the ultimate example of putting the party before the country.
"Brian Cowen should have asked the President for a dissolution of this Dáil."
Mr Kenny said his party will vote against the Government in next week's motion of confidence.