The CEO of Quinn Insurance (QIL), Colin Morgan, has "decided to leave the company".
The company was placed into administration in March after Ireland's financial regulator raised concerns about its solvency.
Mr Morgan, who has been at the firm for seven years, said he was sure it would "recover from current difficulties".
"I feel it is an opportune time for me to pursue other opportunities in my career," he said.
"I have enjoyed the successes and challenges at Quinn Insurance and firmly believe that this business will recover from its current difficulties and, in some form or other, go on to achieve long term success given the strength of the business model and the quality of the people."
Earlier this week the Irish financial regulator said the prices QIL charged were too low for the firm to meet potential claims.
Matthew Elderfield told an Irish parliamentary committee that he was only able to reopen Quinn's UK motor insurance lines after prices went up.
The pricing changes were made by the court-appointed administrators now running Quinn Insurance.
Some of Quinn's rivals in the UK had long speculated that the premiums the firm charged for some business were too low to make financial sense.
The business is now up for sale and 900 staff will be made redundant.
The firm's problems stem from massive losses made when company-founder Sean Quinn made a stockmarket gamble on the now-failed Anglo Irish Bank.