Baroness Vadera was appointed business minister in 2008
Baroness Vadera is stepping down as business minister to take up a new role advising the G20 from Downing Street.
She will focus on the institutions needed to implement the "framework of sustainable and balanced growth" to be agreed this week by the G20.
The former investment banker was a senior Treasury adviser to Mr Brown when he was chancellor and has remained one of his key aides since becoming PM.
A sometimes controversial figure, she became a minister in January 2008.
Mr Brown, speaking in New York, said he was "delighted" she had accepted his invitation to take up the job.
"The G20 is an increasingly important global group. The previous year has shown the vital importance of working together to deliver jobs, growth, and stability. In her new role Shriti will significantly strengthen the UK's engagement with the G20, including working with the Republic of Korea as the next chair," he said.
Business Secretary Lord Mandelson said she had made a "tremendous contribution" to his department.
"She has worked tirelessly to ensure businesses, especially small businesses, are supported through the recession and emerge stronger at the other side," he said.
"Shriti has real passion for the G20 and has done excellent work already promoting international action to tackle the financial crisis. So this is a logical move for her and us."
She will be replaced as minister for competitiveness, small business and enterprise by Lord (Mervyn) Davies, who is also a former City banker.
In her new role - for which she will not get a ministerial salary - she will effectively be employed by the South Korean government - which is shortly to take over the G20 presidency - but would continue to be based in the cabinet office.
Baroness Vadera first hit the headlines in 2001 during the nationalisation of Railtrack after she reportedly called small investors in the company "grannies".
And earlier this year, she was criticised for claiming to see "green shoots" of economic recovery on a day when large job losses were announced.
BBC business editor Robert Peston said: "As Gordon Brown's closest adviser on economic and financial matters, she will be seen as working on what he hopes will be his legacy - a formal structure for creating a more stable global economy."
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