Richard Brasher, the head of Tesco's UK operations, is to quit after only a year in the job.
The move comes after Group Chief Executive Officer, Philip Clarke, said he would "take a much closer involvement in the UK business" following the supermarket firm's first profit warning in 20 years.
"I have decided to assume responsibility as the CEO of our UK business at this very important time," Clarke said.
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"I completely understand why Richard has decided to leave and want to thank him for the great contribution he has made over many years," he added.
Brasher will step down from the board with immediate effect and leave the company in July once he has effected a smooth transition of the UK business to Clarke, Tesco said.
Retail analysts said lacklustre results from the firm's Price Drop campaign and a clash of personalities between Brasher and Clarke were to blame.
Tesco's market share slipped to 29.7% in February from 30.3% a year earlier.
Under-performance in the UK market has prompted Tesco to announce it will revamp its current stores, build fewer mega-stores and focus on its online business.
