David Miliband has been promoted to foreign secretary, giving him a high profile role in Gordon Brown's first government.
The 41-year-old MP is the youngest foreign secretary for 30 years, confirming his reputation as an ambitious politician and potential future prime minister.
Arriving at his new department today Mr Miliband promised to combine patience with purpose and to listen as well as lead.
Mr Miliband said he was "honoured and delighted" at the promotion, which is expected to signal a change in foreign policy from the Brown government.
The new foreign secretary told reporters: "The opportunities and challenges of the modern world require, in my view, a diplomacy that is patient as well as purposeful, which listens as well as leads.
"Those are the virtues that I will be trying to bring to bear in my leadership of the Foreign Office."
He described the Foreign and Commonwealth Office as a "unique global asset" for Britain and promised to deploy it to maximum effect.
After his predecessor was mocked for being "Bush's poodle," Mr Brown has promised to follow a less slavish relationship with George Bush.
Mr Miliband is seen as a politician who is willing to criticise the US administration. As environment secretary he spoke of the importance of leadership from Washington on climate change.
Ms Beckett had already begun to bring climate change under the Foreign Office's remit and her successor will likely continue to push for international action.
His arrival may also signal a new approach towards the Middle East.
Mr Miliband was one of the few Cabinet ministers to criticise Israel's attacks on Hezbollah in 2006. His Jewish background will also allow him to criticise Israel without accusations of anti-Semitism.
He has been awarded one of the largest government jobs after just two years in the Cabinet.
Mr Miliband enjoyed a relatively blemish-free year as head of the Department for Education, Food and Rural Affairs, after first serving as a minister in the Communities Department.
He replaces Margaret Beckett, who was keen to remain at the Foreign Office but was ousted as Mr Brown began his campaign for change.
The new foreign secretary only entered parliament in 2001, as representative for South Shields. He was already embedded in the New Labour project, having worked in Labour's policy unit before the 1997 landslide.
Mr Miliband faced pressure to stand against Mr Brown for the Labour leadership. Eventually he declined to run for either the leadership or deputy leadership.
He will be joined at Cabinet meetings by his brother Ed Miliband as minister for the Cabinet Office.