London Stock Exchange Group boss Xavier Rolet has stepped down with immediate effect, blaming "unwelcome publicity" amid a mounting row over succession plans for the top job.
Mr Rolet had announced last month that he would step down by the end of 2018, but the move sparked a spat between the group and activist investor The Children's Investment Fund Management (TCI), which accused the group's chairman of pushing out Mr Rolet.
Mr Rolet has been replaced by chief financial officer David Warren at the helm, while chairman Donald Brydon said he planned not to stand for re-election in 2019.
Mr Rolet said: "Since the announcement of my future departure on 19 October, there has been a great deal of unwelcome publicity, which has not been helpful to the company.
"At the request of the board, I have agreed to step down as CEO with immediate effect. I will not be returning to the office of CEO or director under any circumstances."
TCI, which owns more than 5% of the LSE, had ordered a shareholder vote for the removal of Mr Brydon and to retain Mr Rolet until 2021.
The LSE Group said it "believed, and continues to believe" that the previous plan to hunt for a successor to Mr Rolet for his departure by the end of 2018 was "in the best interests of the company".
It has now asked TCI to withdraw its demands for a shareholder vote in light of Mr Rolet's decision.
The LSE's leadership row had caught the attention of the Governor of the Bank of England, Mark Carney, who said on Tuesday that he was "mystified" by the tussle.
Mr Carney called for urgent clarity and said he "can't envisage a circumstance where the CEO stays on beyond the agreed period".