Trenwick International's company secretary, who is also its solicitor and a director, is to leave the company.
Joanne Merrick joined the organisation in 1995, but has now been headhunted to join General Cologne Re.
She originally qualified as a solicitor and worked for Lovell White Durrant and McKenna & Co.
Trenwick executive vice president and chief underwriting officer Paul Tester said Merrick had resigned two weeks ago, but had a six-month contractual period.
He said the company would now be recruiting a replacement and other staff.
"Last month we employed a new marine treaty underwriter," he said. "Andrew Hedges used to work on the Liberty marine syndicate.
"We will also be taking on a few more underwriters to grow our portfolio."
Merrick was recently involved in a court case involving former Trenwick chief executive Russell English and underwriter James Trusselle.
The pair won a libel case against Insurance Insider last month. Merrick wrote a letter to editor Peter Hastie, which he read out to the jury in support of his case.
English and Trusselle are considering obtaining an order to make Hastie bankrupt. Mr Justice Gray ordered him to pay them £10,000 damages each, plus combined interest of £847.68 after finding the paper guilty of publishing a defamatory article about them.
The deadline for payment was 4.30pm on 21 February.
English and Trusselle's acting solicitor Jonathan Coad of The Simkins Partnership, said: "My clients are awaiting an explanation about why
Mr Hastie is in breach of court orders.
"One of the options is to apply for an order making him bankrupt or placing his company into liquidation."