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.
More top news
Charity says social media is helping fuel a nation of 'deeply unhappy' children as figures show rise in number hospitalised over self-harm.
It'll become increasing cloudy tonight, with outbreaks of rain in the northwest
Six months on from the referendum, Political Editor Robert Peston takes a road trip to find out what people feel about Brexit now.