The chairman of the Ulster Unionist Party has confirmed that Sir Reg Empey is to resign as party leader.
David Campbell said he had received "formal communication" from Sir Reg and that a meeting to elect a new leader would be held on 22 September.
Sir Reg said he would resign following disappointing results in the general election. He will remain leader until the selection of a new leader.
Nominations for those wishing to be leader must be submitted by 31 August.
Ulster Unionist Fermanagh MLA Tom Elliott has put forward his name for the leadership.
Lagan Valley assembly member Basil McCrea is also expected to enter the race before nominations close.
Mr Campbell said Sir Reg's time as leader had seen "reform and modernisation" of the party.
"As the party's chief negotiator during the All-Party Talks he negotiated the settlement that has led to the peace and stable devolved government that is enjoyed today," he said.
"As a minister at DETI and then at DEL he has been forward in protecting and promoting our economy both at home and abroad, and has always been a constructive partner in the Northern Ireland Executive."