BlackRock, the world's largest asset manager, will keep its biggest European operation and regional headquarters in Britain after Brexit.
The company will move "only very few" roles to expanded offices in the Netherlands and France, a memo to staff seen by Reuters showed.
The commitment by the US firm, which employs around 3,000 staff in Britain and manages around $6.3 trillion worldwide, means it will still have three times as many staff in Britain as in all of the remaining 27 European Union countries combined.
After Brexit, Budapest will become the company's biggest European Union office, with around 450 staff mainly focusing on technology and back-office functions.
The news will be a welcome boost for the City of London and Prime Minister Theresa May's government as the clock counts down to the UK's March 2019 departure from the EU and talks over an exit deal between London and Brussels near a conclusion.
BlackRock had been among the most high-profile financial services firms yet to confirm its Brexit plans, although more are expected to announce them in the coming weeks as most prepare for the worst-case scenario of a breakdown in talks.
BlackRock said it was making two key changes to the way it is structured.
The first will see its Netherlands office take on an expanded role to become the main legal entity for much of the business carried out for EU clients.
The second, confirmed in September, will see its Paris office expand to become a hub for so-called 'alternative' investments such as real estate and infrastructure.
"We have been preparing for the operational, legal and strategic impacts of Brexit for several years, and at this stage, we can tell you that only very few roles will be affected by our decision to extend the regulatory permissions for existing entities in Continental Europe," the memo said.
BlackRock confirmed the contents of the memo.
Total moves out of Britain over the next couple of years would be minimal, a source familiar with the matter said, with the Netherlands office adding 10 to 20 people through moves and local hires, mostly in risk and legal.
The Paris office, which currently houses 40 staff, mostly in sales, would double to around 80 people over that time, but most of those staff would be hired locally, he added.
However, BlackRock appeared to leave the door open to further staff moves depending on how the talks and post-Brexit regulatory regimes change.
"As there is still much political and regulatory uncertainty on the horizon, we remain flexible and continue to monitor all developments very closely. We will keep you posted of further developments," the memo said.