Ulster Unionist Party leader Steve Aiken has announced he is resigning from his position.
The South Antrim MLA became the leader of the party in 2019 after being elected unopposed.
However, it is understood frustration has been growing internally at the party's continued performance.
An assembly election is due to take place next year, and it believed that party members were of the view that a change in leadership was needed before voters went to the polls.
In his letter of resignation, Mr Aiken said he had taken the party as far as he could.
"Despite our successes, it has become clear to me that if we are to achieve the breakthrough in the forthcoming assembly elections, we will need to drive further ahead," he said.
"To represent the brand of Unionism that builds on hope and not fear, and provides a clear, modern, alternative, that will be both the future of our Party and Northern Ireland will require strong leadership.
"Regrettably, however, I believe I have taken our Party as far as it can; to achieve our goals, we now need new leadership.
"Therefore, after due consideration, I would wish you to accept my resignation as Party Leader, effective from 10am on May 10th, 2021.
"I will not be retiring from politics and I will be dedicating myself fully to support our new Party Leader, our Party, but above all to the people of South Antrim."
LETTER FROM STEVE AIKEN OBE MLA
— Ulster Unionist (@uuponline) May 8, 2021
UUP chairman Danny Kennedy thanked Mr Aiken for his services as leader of the party and said he can take "considerable pride" in his "many achievements as our party leader and the necessary reforms to our structures brought under your watch".
"Without doubt, you have always sought to lead from the front," he said in a statement.
"It is clear from your letter that you passionately believe in the future development of our party and its importance and relevance within the political life of our beloved Province.
"I am particularly pleased that you have clearly indicated your willingness to continue as part of our team and I have no doubt that you will play a central role as we seek to restore our political fortunes.
"On a personal note, it has been my honour to serve you as Party Chairman and I genuinely thank you for that opportunity. I have witnessed at close quarters your dedication to duty and the dignity you have displayed at all times as Party Leader, even in challenging circumstances."