An official in Johnson's Downing Street office confirmed the prime minister would announce his resignation later. The official spoke on condition of anonymity because the announcement had not yet been made.
Johnson had rebuffed calls by his Cabinet to step down in the wake of ethics scandals. He gave in after more than 40 ministers quit his government and told him to go.
It was not immediately clear whether Johnson would stay in office while the Conservative Party chooses a new leader, who will replace him as prime minister.
Minutes before the news broke, Treasury chief Nadhim Zahawi called on Prime Minister Boris Johnson to resign just 36 hours after Johnson put him in the job, while another newly appointed Cabinet minister quit her post.
Zahawi said Johnson knew "the right thing to do" was to "go now."Zahawi was appointed late Tuesday to replace Rishi Sunak, who resigned saying he could no longer support Johnson after a series of ethics scandals.
Education Secretary Michelle Donelan, who was also appointed on Tuesday following the resignation of her predecessor, announced her resignation Thursday morning.
Johnson had rejected clamors for his resignation, digging in his heels even as dozens of officials quit and previously loyal allies urge him to go after yet another scandal engulfed his leadership.
A group of Johnson's most trusted Cabinet ministers visited him at his office in Downing Street Wednesday, telling him to stand down after losing the trust of his party. But Johnson instead opted to fight for his political career and fired one of the Cabinet officials, Michael Gove, British media reported.
It is rare for a prime minister to cling on to office in the face of this much pressure from his Cabinet colleagues. The Guardian's frontpage on Thursday called him "Desperate, deluded."
"He's breached the trust that was put in him. He needs to recognise that he no longer has the moral authority to lead. And for him, it's over," Scottish National Party leader Ian Blackford told The Associated Press.
Johnson, 58, was known for his knack for wiggling out of tight spots. He remained in power despite allegations that he was too close to party donors, that he protected supporters from bullying and corruption allegations, and that he misled Parliament and was dishonest to the public about government office parties that broke pandemic lockdown rules.
But recent disclosures that Johnson knew about sexual misconduct allegations against Chris Pincher, a Conservative lawmaker, before he promoted the man to a senior position turned out to be the last straw.
Last week, Pincher resigned as deputy chief whip after complaints he groped two men at a private club. That triggered a series of reports about past allegations leveled against Pincher - and shifting explanations from the government about what Johnson knew when he tapped him for a senior job enforcing party discipline.
Health Secretary Sajid Javid and Treasury chief Rishi Sunak resigned within minutes of each other Wednesday over the scandal. The two Cabinet heavyweights were responsible for tackling two of the biggest issues facing Britain - the cost-of-living crisis and COVID-19. - Marca.com
