Sir Stuart Rose is to leave Marks & Spencer by March next year and will take a pay cut of a quarter when he becomes non-executive chairman at the end of July.
M&S said it had hired headhunters JCA to find a new chairman, and its nomination committee will meet in the next two weeks to discuss the type of candidate they want.
The retailer said that the swift hiring of Marc Bolland, the incoming chief executive, who joins from Morrisons on 1 May, had enabled it to bring forward Sir Stuart's leaving date.
Sir Stuart, its executive chairman, said this month at the Retail Week Conference that he was likely to step down early, although his "drop-dead date" was 31 July 2011.
Sir David Michels, the deputy chairman of M&S, said that Mr Bolland had been "consulted" about Sir Stuart's departure date, but stressed it was not his decision for him to step down early.
M&S has recently come under pressure from shareholders to reduce Sir Stuart's pay when he becomes non-executive chairman.
The chairman is on a salary of £1.16m, but this will be reduced by 25 per cent to £875,000 from 31 July. Mr Bolland will start with a salary of £975,000 but, controversially, he could earn up to £14.8m in his first year.
Sir David said that initially Sir Stuart – who joined M&S as CEO in 2004 to help fend off a takeover bid from Sir Philip Green – will be involved in assisting Mr Bolland to "get to know the company he knows and loves". But he added that over time, his working schedule was likely to be reduced: "I reckon that the chair of M&S is at least a three-day-a-week job."
Sir David had hinted he was interested in the chairman's role, but ruled himself out earlier this year due to work commitments, making it likely a new chairman will be hired externally.
Asked about Sir Stuart's legacy at M&S, he said: "He saved the company and kept it independent [in 2004]. I think he has made us a relevant brand for the 21st century."