David Trimble has resigned as leader of the Ulster Unionists following his party's worst-ever results in the Westminster elections.
It has reduced the Ulster Unionists' representation in the House of Commons to one. The DUP now has nine seats.
He held a private meeting this morning with the party President Lord Rogan and chairman James Cooper, who had earlier expressed bitter disappointment at the election result.
Mr Trimble, who took over as Ulster Unionist leader nearly ten years ago, told them he did not wish to continue as leader.
The party is expected to call a meeting of the Ulster Unionist Council within a month to elect a new leader.
He earlier outlined the reasons which he feels brought about the loss of his seat and three of his party colleagues in the Westminster elections.
Mr Trimble said the British government's indulgence of republican manoeuvring since the Good Friday Agreement was signed was a contributory factor to the collapse of his party's vote.
And he said there was total disgust in the unionist community with republicans.
The Taoiseach, Bertie Ahern, said he was sorry to hear the news of David Trimble's resignation.
He said Mr Trimble had made a tremendous contribution during and after the Good Friday Agreement.
The British Prime Minister, Tony Blair, said history would show that without David Trimble's period as leader of the Ulster Unionist Party, Northern Ireland could never have become the changed place it is today.
Mr Trimble, along with the former SDLP leader John Hume, won the Nobel Peace Prize in 1998.
