Dame Karen Pierce was appointed UK Special Envoy to the Western Balkans in February 2025, and was previously British Ambassador to the USA (2020-2025).

Prior to Washington, Karen was the United Kingdom's Permanent Representative to the United Nations in New York (2018-2020). She served as the Director General for Political Affairs and Chief Operating Officer of the Foreign and Commonwealth Office in London from 2016, having worked in the FCO since 1981.

She has worked in Tokyo (1984-1987), and in Washington as the Private Secretary to the British Ambassador to the United States (1992-1995). From 1996 to 2006, Karen held several positions in London including Team Leader for Ukraine, Belarus and Moldova, Deputy Head of Eastern Adriatic (Balkans) Department, and Head of Afghanistan Political Military Unit after 9/11. She returned to the Balkans as Balkans Coordinator from 2002 to 2006.

In 2006, Karen moved to New York as the Deputy Permanent Representative and Ambassador at the UK Mission to the UN. In 2009, she returned to London to become the Director of South Asia and Afghanistan Department and the UK's Special Representative for Afghanistan and Pakistan. In Geneva, she was the Ambassador and Permanent Representative to the UK Mission to the United Nations (2012-2015). Karen was the UK's Ambassador to Afghanistan (2015-2016).

Since 2020, she has been a Governor of the Ditchley Foundation, a charity founded to support the UK/US Transatlantic Alliance.