Baroness Catherine Ashton on Monday formerly assumed her duties as the European Union's new trade commissioner following Peter Mandelson's return to British politics, dpa reported.
"I am delighted and very proud to have been asked to serve as commissioner, to be a part of the European response to the global challenges we face," Ashton said shortly after her appointment.
An economics graduate, the 52-year-old British Labour politician will represent the EU in negotiations at the World Trade Organization (WTO).
Ashton was nominated by British Prime Minister Gordon Brown on Friday, in agreement with European Commission President Jose Manuel Barroso, raising the total number of women in the 27-strong EU executive to 10.