Spencer Livermore has been appointed director of political strategy at No 10.
The 32-year-old has unrivalled access to the new Prime Minister and will play a key role in shaping the direction of the Brown government.
Mr Livermore was ranked seven in this year’s Independent Pink List, making him the most powerful gay person in UK politics.
He read economics and politics at the London School of Economics before joining the Labour Party economic research unit in 1997.
Mr Livermore was appointed as a Special Adviser to Chancellor Brown in May 2005.
His elevation as the Chancellor’s senior political adviser following Ed Miliband’s departure was evidence of a close working relationship that will continue in No 10.
“He’s brilliantly clever, but also very engaging and charming – a good contrast to Gordon, who’s always very intense,” a friend of Mr Livermore told The Guardian.
He is reportedly a keen film fan and supports Fulham FC.