The London Stock Exchange said its chief executive, Xavier Rolet, plans to step down by the end of 2018 after almost a decade in the top job.
The French national’s departure will take place just before Britain formally leaves the European Union, in March 2019.
The LSE Group gave no reason for Rolet’s move. It added that the search was already on for a successor.
"The board is now initiating a process to find a successor and will work closely with Xavier to ensure a smooth transition process as the group continues to execute on its successful growth strategy," a statement said.
Rolet took the helm of the LSE Group in May 2009, replacing Dutchwoman Clara Furse who had begun the process of steering the group through the global financial crisis.
Prior to joining, he headed the French operations of Lehman Brothers shortly before the collapse of US investment group that spread havoc through the world's financial system.
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As CEO of the LSE Group, Rolet has overseen huge growth in the company’s market value to nearly £14 billion from £800 million.
“I am extremely proud of all we have done together in just under a decade to turn LSEG into a truly global financial market infrastructure group,” said Rolet.
Under Rolet’s watch, the company purchased US asset manager Russell for $2.7 billion to diversify and boost its business in the United States.
It additionally bought LCH.Clearnet, the British clearing house.
However, a planned merger with Germany’s Deutsche Boerse collapsed in March after EU regulators blocked it on competition concerns. Rolet had been due to step down as LSE boss if the blockbuster tie-up had gone through.
The London exchange's chairman, Donald Brydon, on Thursday hailed Rolet's "remarkable achievements" by saying that "under his leadership, LSE Group has been transformed in scale to become a truly diversified and international leader in financial markets infrastructure."
The LSE is seen as one of the front-runners to win part of Saudi Aramco’s initial public offering – expected to be the largest in history – and Rolet has been pushing hard to land it.
He travelled with British Prime Minister Theresa May earlier this year to Saudi Arabia, with the pair meeting the kingdom’s sovereign wealth fund, which is expected to be a major decision-maker in the listing process.
He is also thought to be working on a new type of listing structure that would make it more attractive for the oil giant to join the bourse.
Speaking on Wednesday, Rolet warned that more British firms would move business to EU countries should Britain fail to hammer out a post-Brexit transition deal by the end of the year.
"In the absence of certainty in the next few months, the businesses, the CEOs, the boards the executive committees of many companies that are based here will have to start acting on worst case scenarios," the 57-year-old said in a speech made at Britain's parliament.
Mrs May has backed a two-year transition period to ease the impact on the UK economy, but she is beset by divisions within her own Conservative party and talks with Brussels are stalled over the size of the country's exit bill.