This file photo taken on April 29, 2019 shows Karen Pierce, UK ambassador to the UN, speaks during a Bloomberg Interview in New York, US. (CHRISTOPHER GOODNEY / BLOOMBERG)

Prime Minister Boris Johnson’s government named Karen Pierce as the UK’s new ambassador to the US, filling a crucial post as it seeks to burnish post-Brexit ties with its closest ally.

Pierce, 60, will be the UK’s first female ambassador to Washington, and will start her new role as soon as the US government approves her appointment

Pierce, 60, will be the UK’s first female ambassador to Washington, and will start her new role as soon as the US government approves her appointment, Johnson’s spokesman, Jamie Davies, told reporters on Friday. Pierce will move to Washington from New York, where she’s been the envoy to the United Nations for the past two years.

“It is a time of huge opportunity for the friendship between the UK and US and I am delighted that Karen Pierce will take forward this exciting new chapter in our relationship,” Foreign Secretary Dominic Raab said in an emailed statement. “We’re proud to be sending to Washington such an outstanding diplomat, and I warmly congratulate her on her appointment.”

The UK’s previous ambassador, Kim Darroch, quit in July after falling out with President Donald Trump, just one of a series of recent flash-points between the two sides that have come at a pivotal moment. Having left the European Union last month, Britain is trying to strengthen links with the world’s biggest economy by striking a trade deal this year.

The two governments have clashed in recent weeks on issues including Iran, UK plans to tax American technology companies, the involvement of a US diplomat’s wife in a fatal car accident in England and the role of Huawei Technologies Co. in the UK’s next-generation broadband networks.

“The UK has an excellent relationship with the United States and Dame Karen’s ability as a diplomat is proven by her career,” Davies said when asked if Pierce’s first task would be to heal the rift between the two countries.

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‘Uniquely Dysfunctional’

Pierce must tread carefully while still fighting the UK’s corner. Her predecessor resigned after cables in which he called the Trump administration “inept” and “uniquely dysfunctional” were leaked, sparking a major diplomatic row. Trump froze out the envoy, saying he’d no longer deal with him.

Johnson -- then the front-runner in the race to succeed Theresa May as prime minister -- notably failed to back Darroch, feeding into the envoy’s decision to resign. In a televised debate, Johnson would not commit to keeping Darroch in his job, in sharp contrast to the endorsements and support the ambassador received from May and other senior politicians.

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Pierce joined the Foreign Office in 1981 and has previously served as ambassador to Afghanistan. She also appears to have made a good impression on Trump during her role as UN ambassador. She attended a dinner with the president in early December, and the Mail on Sunday reported later that month he described her as “fab.”