In a statement, PizzaExpress said managing director Zoe Bowley and CFO Jo Bennett will report directly to group chairman Allan Leighton until a successor is appointed.
Campbell was appointed CEO of PizzaExpress in November last year.
It followed a major recapitalisation and restructuring of the business that also saw it deleverage its debts, provide new liquidity and divest its mainland China business.
Campbell joined PizzaExpress following a two-year stint as executive chairman at Bill’s.
He previously led Wagamama for four years between 2013 and 2017.
Campbell's departure follows a recent trading update from PizzaExpress in which he described 2021 as a 'transformational' year for the brand
The group reported strong results for the year to 5 September 2021, achieving revenues of £182.5m and EBITDA of £22.2m for the period.
Sales outperformed the CGA Peach market tracker for every week but one since the return to unrestricted dining on 19 July 2021 (+3.7% ahead of the market for the 7 weeks 19 July 2021 to 5 September 2021).
Campbell also revealed that following the long-term refinancing of the group, plans are 'well underway' to open 50 new restaurants over the next three years, beginning later this month with a new Cannock site in Staffordshire.