Lloyd's of London says it will establish a new European subsidiary in Brussels to avoid losing business when the UK leaves the EU.
"A subsidiary office will be opened in Brussels with the intention that it will be operational for the January 1 renewal season in 2019," it said.
The company's continental business generates 11% of its premiums.
Lloyd's of London's chief executive Inga Beale told the BBC's Today programme Brussels had certain key attractions: "What we were after was some jurisdiction that had a really robust reputation for regulation, we also wanted to be able to access talent and we wanted really good accessibility.
"Brussels came out top of our list."
However, she stressed that the Brussels office was an additional base, simply an EU subsidiary, and that the number of jobs affected was less than 100.
The company has around 700 London employees, but the market it runs involves more than 30,000.
Other financial institutions have also said they are thinking of moving some business within Europe.
Several investment banks, including Bank of America, Barclays, and Morgan Stanley are considering relocating staff to Dublin. Frankfurt, Madrid and Amsterdam are also likely to benefit. HSBC is expected to move significant numbers of employees to Paris.
Lloyd's of London also announced it had made a profit of £2.1bn in 2016, the same as for the year before.
It said conditions over the course of the year had been "extremely challenging". There were £2.1bn of major claims - the fifth highest since the turn of the century - which was due mainly to Hurricane Matthew and the Fort McMurray Wildfire in Canada.
However, the company added that its results had been helped by "significantly improved" investment returns.
Lloyd's, one of Britain's oldest institutions, is the world's leading insurance and reinsurance market.
It focuses on specialist markets, such as marine, energy and political risk, but also branches out into more unusual areas, such as insuring comedian Ken Dodd's teeth.