Speaking at a news conference at her official residence in Edinburgh, Bute House, Sturgeon said she wrestled with the decision, but that the pressure of the job was relentless and that she is a human being as well as a politician.

Sturgeon, who has led the country’s devolved government and the Scottish National Party for eight years, has faced months of controversy over a law that makes it simpler for people to change their gender on official documents.

The decision caught political observers by surprise, despite the ongoing controversy over the gender recognition measure. She had vowed to take the British government to court over its decision to block the law and argued that the Conservative UK government was making a “profound mistake” by vetoing the Gender Recognition Reform Bill.

But the measure was only one controversy in a career where Sturgeon has been noted for rarely putting a foot wrong.

She had been lauded for her response, for example, to the COVID-19 pandemic, where she won praise for her sober, straight-talking abilities.

That catapulted the idea of Scottish independence from the United Kingdom — the long-held dream of Sturgeon’s nationalist government — back up the political agenda.

Scotland is part of the UK but, like Wales and Northern Ireland, has its own semi-autonomous government with broad powers over areas including health care.

The deputy first minister John Swinney wrote on Twitter: “I am very sorry Nicola Sturgeon has decided to step down as first minister and as SNP leader.

“She has given outstanding leadership to our country, government and party.”

He said she has “achieved much” particularly with her leadership during the COVID pandemic.

“She has delivered breath-taking electoral success, winning every election during her leadership, and securing two Scottish Parliament victories,” he added.

“It has been my privilege to support her as deputy first minister. She has my warmest good wishes for the future and heartfelt thanks for all that she has done for Scotland, for the cause of Independence and the Scottish National Party.”

Alex Salmond, the Alba party leader and Nicola Sturgeon’s predecessor, said he “feels for her personally” on the day of her resignation.

He saids there are two questions for the future — the first around the strategy for independence and the second addressing the issue of who will take her place.

“The previously accepted referendum route has been closed and the defacto referendum/election proposal is now, at best, up in the air,” he said. “It is to be hoped that those voices which wish to reunite the national movement emerge to win that contest,” he added.

Meanwhile, politicians across the political divide have also been reacting to Sturgeon’s resignation announcement.

British Prime Minister Rishi Sunak thanked her “for her long-standing service”, adding on Twitter: “We will continue to work closely with the scotgov on our joint efforts to deliver for people across Scotland.”

Plaid Cymru leader Adam Price said she was “a once in a generation politician, driven by an unwavering passion for her country”.

Scottish Labour leader Anas Sarwar said Sturgeon was an “able politician” and led Scotland through some of the most “challenging times” in recent history.

While Sinn Fein Vice President Michelle O’Neill paid tribute “to the huge strides she has made in advancing the campaign for Scottish independence, the strong stance against Brexit and the undermining of devolution by the Tories in London”.