Tom Elliott is to quit as Ulster Unionist leader after accusing party critics of not giving him a chance.
He dramatically announced that he will not be seeking re-election at the party's annual meeting later this month.
Mr Elliott, a member of the Northern Ireland Assembly who took over the leadership in the summer of 2010, claimed: "I am well aware that some people have not given me a fair opportunity at developing and progressing many initiatives. Some of this obstruction and hostility began immediately following my election as leader and has been relentless since then. However I accept that is part and parcel of politics."
His leadership has been under pressure since the party's dismal performance in the Assembly elections in May last year - which followed an equally disastrous General Election when the party failed to win a single seat.
In a statement, Mr Elliott said: "Following my election as leader I set about improving internal party structures, since then I have amended the party rules, including discipline; significantly increased internal party communications; negotiated a move for new party headquarters and strengthened our staff structure. I have also been successful in leading the political field by making a start to reviewing the government structures and reducing the over-governance of Northern Ireland."
Mr Elliott took over the leadership from Sir Reg Empey in August 2010. He will remain a member of the Assembly for Fermanagh-South Tyrone.
The election of the new leader will take place on March 31 and Basil McCrea and Danny Kennedy are likely emerge as some of the front-runners for the job.
Mr Kennedy was one of the first senior members to wish him well. He said Mr Elliott had given loyal and dedicated service.
He added: "I want to pay a warm and genuine tribute to his many fine qualities of honesty, integrity and leadership which he has displayed throughout his tenure as leader."
The Unionist Unionists were once the most powerful political party in Northern Ireland, but now trail far behind the Democratic Unionist Party for the traditional Unionist vote. Senior party officials had been involved in talks with the DUP with the aim of agreeing some sort of electoral pact for future elections in an attempt to strengthen the overall unionist vote.