Jeremy Blood, the former boss of brewing giant, Scottish & Newcastle, who in March took over as temporary chief executive, is to step down after a brief handover period.
His role will be taken on by interim chairman, Bob Ivell, until a permanent chief executive is found.
The group, which operates 1,600 sites in Britain, including All Bar One and O’Neill’s, has seen lacklustre trading in recent months. Analysts had already voiced concerns that management upheaval could be upsetting business.
Chairman Simon Burke, and chief executive, Adam Fowle, announced their shock departures earlier in the year.
Mr Fowle had been at the helm for less than two years, while Mr Burke took over from John Lovering less than six months ago.
It has been reported that Mr Burke’s departure came after he fell out with billionaire activist investor and owner of Tottenham Hotspur football club, Joe Lewis, who owns nearly a quarter of the shares in the company.
Mr Lewis recently tried to buy Mitchells, with a second bid worth £940 million (€1.066m), but his offers were rejected as a “significant undervaluation” of the business. The company currently has a market valuation of about £1 billion after shares rose 3% Thursday.
Irish racehorse magnates, John Magnier and JP McManus, hold a 20% stake in the company
The company’s recent performance has been quite weak, with like-for-like sales slowing to 0.5% in the nine weeks to September 17 from 2.8% during the summer.