Sir Reg Empey is formally to stand down as leader of the Ulster Unionists next week, leading to a leadership election next month.
The East Belfast Assembly member announced his intention to resign the leadership in the wake of a poor Westminster election showing.
He failed to oust the sitting DUP MP William McCrea in South Antrim while his colleagues failed to win any House of Commons seats for the first time in a century.
Announcing his intention to go Sir Reg called on DUP leader Peter Robinson also to consider quitting in order o help unionism to consider a fresh approach to politics.
"Perhaps both of us could leave the stage and allow a fresh leadership to look at the situation anew, without any baggage," he said announcing his intention to quit in May.
"If I can put myself in this position having failed to win a seat I'd never held, perhaps somebody who held their seat but lost it might think about his position."
In response, the DUP criticised Sir Reg as an obstacle to unionist unity and called for the search for greater co-operation to "step up a gear".
Sir Reg's departure has been brought forward to facilitate the seeking of nominations in advance of the leadership election.
Candidates require 35 signatures from a spread constituencies to enable them to stand.
The election for the post will mostly likely be held on Wednesday, September 22nd at Belfast’s Waterfront Hall.