Philip Clarke's departure as Tesco chief executive follows a disappointing set of sales figures for the first half of this year, the company said in a statement.
The supermarket giant said "challenging" trading conditions and a weaker than expected market meant "sales and trading profit in the first half of the year are somewhat below expectations".
The company's chairman Sir Richard Broadbent paid tribute to Mr Clarke's achievements but said it was time for "a new leader with fresh perspectives and a new profile".
Mr Clarke said it was "the right moment" to hand over the reins and that he was "delighted" that Unilever executive Dave Lewis had been chosen as his replacement.
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