BT chief executive Ian Livingston is to step down in September to become a UK government trade minister.
David Cameron announced the move at Prime Minister's Questions, saying Mr Livingston would succeed Lord Green - the former HSBC chairman - who will stand down at the end of the year.
Mr Livingston has been BT chief executive for the past five years.
Mr Cameron said: "I believe he will bring huge talent to a vital national effort."
In a statement to the stock exchange, Mr 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... 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."
Mr Livingston will join the House of Lords prior to taking up his front-bench government post in December.
Source: BBC News - Business http://www.bbc.co.uk/news/uk-politics-22972193#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa