M&B said a search process is underway to identify a successor, which will be announced “in due course”.
The group said it will continue to focus on its strategy to develop its brands under the interim leadership of Jeremy Blood, who is currently a non-executive director on the Board.
Interim M&B chief executive
Blood will act as interim chief executive until a permanent successor is appointed, with Fowle remaining at M&B for a period to ensure “an orderly and effective transition”.
M&B chairman, Simon Burke, said: "Adam has made a significant contribution over a number of years to Mitchells & Butlers and in particular in the past two years, developing and leading the strategic change the company has undertaken whilst maintaining a strong operational performance in challenging conditions.
“He leaves the company in a much stronger position than when he took over as Chief Executive and we wish him all the best for the future."
"Jeremy has significant industry and corporate experience and I look forward to working with him during this interim period."
The PMA Team, editor of BigHospitality sister publication The Morning Advertiser, said: “The decision by Fowle is another shock given M&B has, as yet, only opened a handful of new sites in retail parks and the wider strategy is still in its relatively early stages.
“Observers are speculating that Fowle has grown tired of the boardroom strife that has been a constant at M&B over the past few years — or else has been unable to strike up a working relationship with new chairman Simon Burke.”