Dame Karen Pierce, the UK’s permanent representative to the UN, has been appointed Britain’s ambassador to Washington, becoming the first woman to hold the position – the most prominent in the diplomatic service.

Pierce, a career diplomat who joined the Foreign Office in 1981, faces an arduous task to restore frayed relations with Donald Trump’s administration after the previous ambassador, Kim Darroch, felt forced to resign over leaked cables that revealed he made uncomplimentary personal remarks about the US president.

Tensions between London and Washington worsened after the British government’s decision to give the Chinese telecoms corporation Huawei partial access to the UK’s 5G network. The decision was taken in defiance of pressure from the White House and reportedly led to a difficult phone call between Trump and Boris Johnson days later.

The US president was “apoplectic”, according to a report in the Financial Times, despite Foreign Office officials believing they had squared the decision with the US intelligence community before making the announcement.

Since joining the Foreign Office, Pierce has been posted to Tokyo, the Balkans and Geneva. She served as the UK’s ambassador to Afghanistan in 2015 and 2016. She became political director at the Foreign Office, a leading domestic diplomatic position, before heading to the UN. There she has regularly crossed swords with Russia over its conduct in the Syrian civil war, arguing its support for Bashar al-Assad’s regime has weakened Vladimir Putin’s moral authority.

Pierce has a blunt speaking style when necessary and fought back strongly against suggestions that British influence at the UN was on the wane because of Brexit.

Pierce said she was “honoured” to have been asked to take up the post. “I think it is the UK’s single most important relationship. There is a deep bond between Britain and the US, built on many pillars,” she said.

“We have a fantastic cross-government team across the US and I look forward to working with them to strengthen and even further deepen the special relationship between our two countries and peoples.”

Dominic Raab, the British foreign secretary, added: “At a time of huge opportunity for the friendship between the UK and US I am delighted that Karen Pierce will take forward this exciting new chapter in our relationship. We’re proud to be sending to Washington such an outstanding diplomat, and I warmly congratulate her on her appointment.”

Although Trump admires Johnson personally, and has welcomed Brexit, a raft of issues – including climate change, the Iran nuclear deal and a UK digital tax – could sour relations and make US-UK trade talks, due to be negotiated this year, more difficult.

The UK in turn feels wounded that it was not consulted prior to major moves by Washington in the Middle East, such as the US troop withdrawal from Syria or the attack that killed the Iranian general Qassem Suleimani.

Johnson decided to shelve an early visit to Washington to concentrate on domestic issues. The prime minister has good relations with the Trump family, including the president’s son-in-law Jared Kushner.

In a presidential election year, Pierce will also need to maintain links with senior Democrats, even if the odds move towards the prospect of a second Trump term.

Her successor at the UN will have to fend off calls for the UK to give up its seat on the security council, which is seen by African and South American states as a post-second world war anachronism.

Pierce, whose husband works in the Treasury, grew up in Preston in Lancashire, “reading boys’ books and drawing fighter jets in art class”.

Her northern accent was stripped away at a young age by elocution lessons, partly to help with a childhood stammer. She has an ability to switch from a frank informality to full diplomatic sobriety in the space of a minute.

In a recent Guardian profile Pierce identified the decisive moment in her early life as “sitting at the breakfast table aged about 11 and staring at a photograph of an African-American diplomat boarding a battleship in some sunny, foreign place.”

That woman was almost certainly Eleanor Hicks, one of the very few African-American women who served in senior roles abroad for the US state department in the early 70s. Hicks was the US consul in Nice, and to Monaco. Her style, singing ability and fashion sense meant she was regularly profiled in colour magazines around the world.

“I definitely remember being attracted by the blue of the sky, the white of her suit and her black skin, the grey and the whites of the sailors,” Pierce says. “It was a stunning photograph. I didn’t understand where it was, but it wasn’t Preston.”