BT Group's chief executive Ian Livingston is to leave the telecoms giant to take up a role in government as minister of state for trade and investment.
Livingston had been BT's chief for the past five years and will be replaced by BT's chief executive of BT retail, Gavin Patterson.
Patterson joined BT in 2004 and is a board member. He will take over as chief executive of BT Group in September.
Livingston will succeed Lord Green as minister of trade and investment.
"Ian has done a tremendous job in transforming BT. His decision to accept a government post demonstrates the sense of public service which many of us know to be characteristic," said the telecoms giant's chairman, Sir Michael Rake. "He leaves behind him a very capable team, one which will take forward the strategy that has served BT well and which lays out the path to further success."
In a statement, Livingston said: "I am honoured to have been asked by the prime minister to take on the role of minister for trade and investment, with a remit of helping the growth of British companies and the country's future economic success.
"It has been an incredibly hard decision to leave BT at such an exciting time. However, the opportunities ahead and the strength of the management team that Gavin will lead mean that the company is in a great position.
"I am immensely proud to have led this company over the last five years. We have made huge progress over the last few years but I know there is still so much more that BT can and will do," he added.
Livingston will join the House of Lords before taking up his front-bench government role in December 2013.