UK Prime Minister Boris Johnson on Friday appointed the first-ever female ambassador to the United States.

Dame Karen Pierce, currently ambassador to the United Nations, will succeed Sir Kim Darroch as HM ambassador in Washington.

Downing Street described her as “one of the UK’s most experienced senior diplomats”, adding: “The prime minister is clear that she is an outstanding and accomplished diplomat and he is delighted that she will be representing us in Washington.”

Dame Karen will take up her post once her appointment has been formally agreed by Washington.

Pierce is well suited to the task as she is a former UK deputy permanent representative at the UN in New York.

She also represented the UK at the UN and the World Trade Organisation in Geneva.

She is leading a relatively new team since her deputy, Jonathan Allen has only been in New York since April. She is to succeed Matthew Rycroft, who is to return to the UK as permanent secretary to the Department for International Development. Rycroft will replace Mark Lowcock, who has taken up a senior humanitarian coordinating role at the UN.

Pierce’s arrival also comes at a time when the effectiveness of the UN is under greater question than ever. The new UN secretary, António Guterres, is starting to implement a reform programme aimed at reducing bureaucracy.

(With inputs from agency)