Pierce is the first woman appointed to this role, and is uniquely suited for the position having previously served as Deputy Permanent Representative to the UN in New York, and more recently as the Permanent Representative to the UN in Geneva, the UK Mission to the UN said in a statement.
Britain's Permanent Mission to the United Nations did not give any reason for appointing Pierce as new ambassador to the world body, which comes days after it failed to get its judge Christopher Greenwood elected to the International Court of Justice (ICJ) after India's Judge Dalveer Bhandari consistently received nearly two-third of the votes in the UN General Assembly.
Bhandari was on Tuesday re-elected to the ICJ as the UN General Assembly overwhelmingly threw its weight behind him, forcing Britain to withdraw its candidate from the hard- fought race to the world court.
This is for the first time in 70 years that Britain would have no judge in the 15-member panel of the ICJ.
Political analysts and editorials in British media have described it as a diplomatic failure of the Therasa May government.
"Britain has a proud history of working for positive change through the United Nations, not least in addressing the problems in Libya and Syria," British Foreign Secretary Boris Johnson said in a statement without addressing the reason for sudden replacement of Rycroft.
Rycroft has been in the post since 2015 and will handover in January 2018 when he returns to London to take up his new role as Permanent Secretary at the Department for International Development.
"I know Karen has the diplomatic skills, energy and patience to continue this vital work, and I congratulate her on her appointment," Johnson said.
In a statement, Pierce said the UK had long been a strong supporter of the UN and its role at the heart of the global rules-based international system at a time when it is coming under challenge.
"Through our role as a permanent member of the Security Council and position as the UN's third largest donor, the UK will continue to work with others to tackle the pressing security, stability, development and prosperity challenges of today," she said.
"Our security and economic interests depend to a large extent on a strong and effective United Nations...I undertake to ensure we are an active force in New York for progress and partnership," Pierce said.
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
)