Kevin Spencer has resigned suddenly as managing director of Lloyd's guaranteeing brokers Edgar Hamilton and Wellard after just 18 months in the position.
Spencer said it was an amicable split and he would be staying with the company until May 1 to complete outstanding projects.
But he is moving to pursue "other projects", which will include internet brokers Cast Systems and Brokerline, in both of which he has shareholdings.
Spencer, who has been with EHG for 15 years, said there were other "major projects" he was involved with and he would announce the details of these as soon as the relevant deals were signed.
He added: "I will continue to be working closely with EHG chairman Terry Wellard in companies in which we are both involved."
Spencer was brought in as MD to turn round the fortunes of the group. He said that task was now largely complete and the company is in profit.
There are no plans to replace him, though Wellard is likely to become more "hands-on", a spokeswoman said.
Wellard said: "Our strong position trading forward can, in part, be attributed to the energies and re-invention of strategies introduced by Kevin. We'll all be sorry to see him go."
EHG is also planning to set up a new Lloyd's syndicate writing private car, small fleets and household business. It is due to start trading from July, once investment has been raised and regulatory hurdles have been overcome.