Ian Livingston has resigned as CEO of BT to become Minister of Trade and Industry.
Livingston who has driven an aggressive cost cutting and business transformation strategy at the company will be replaced by Gavin Patterson, chief executive of BT Retail.
Livingstone, whose departure was unexpected, will hand over the reins in September.
In five years as CEO he reorganised the BT Services division, which was running at a heavy loss, reduced headcount by 30,000 and embarked on an aggressive media strategy, taking on Rupert Murdoch's Sky organisation.
BT investors backed the strategy, with company shares rising 50 percent in the last 12 months.
Delivering annual profits of £2.5 billion last month, Livingston said, "We are doing what we said we would do. In an environment where it is easier to focus only on the short-term, we are investing in our future and delivering growth in profits and dividends.
"We are driving fibre across the UK, launching high quality sports channels, investing in the high-growth regions of the world and will use our WiFi capabilities and 4G spectrum to make sure our customers will be the best connected."
Commenting on his new role, the BT CEO 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," Livingston said.
"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," he added.