The Prime Minister quickly filled the vacant Cabinet posts with Education Secretary Nadhim Zahawi moving to Number 11 and key ally Steve Barclay appointed as Health Secretary.
Minister of State for Universities Michelle Donelan will take on Nadhim Zahawi’s old role, Downing Street said.
Accepting the two resignations a bullish Mr Johnson vowed to “continue to deliver” his Government’s plans but a snap YouGov poll on Tuesday night suggested 69 per cent of Brits now think the Prime Minister himself should resign.
On Tuesday, in the space of less than 20 minutes, Mr Sunak and Mr Javid quit the Cabinet citing concerns over the Prime Minister’s leadership and the standards of his Government.
Their departures plunged Mr Johnson’s premiership into its biggest crisis yet.
Bim Afolami also resigned as a vice chair of Conservative party while speaking to TalkTV.
But most Cabinet ministers remained loyal to Mr Johnson including Deputy Prime Minister and Justice Secretary Dominic Raab, Home Secretary Priti Patel and Business Secretary Kwasi Kwarteng.
Culture Secretary Nadine Dorries backed the PM, tweeting: “I’m not sure anyone actually doubted this, however, I am 100 behind @BorisJohnson the PM who consistently gets all the big decisions right.”
Jacob Rees-Mogg has confirmed he will continue to back Boris Johnson as Prime Minister.
The Brexit Opportunities Minister told Sky News: “The Prime Minister won a large mandate in a general election, a vote of the British people and that should not be taken away from him because a number of people resign.”
In his resignation letter, Mr Sunak said “the public rightly expect government to be conducted properly, competently and seriously”.
He added: “I believe these standards are worth fighting for and that is why I am resigning.”
Boris Johnson responded saying he was “sorry” to have received Mr Sunak’s resignation letter and praising his “outstanding service”.
In a letter, the Prime Minister wrote: “Dear Rishi, I was sorry to receive your letter resigning from the Government.
“You have provided outstanding service to the country through the most challenging period for our economy in peacetime history”.
He praised tax cuts and the furlough scheme before concluding: “I have enormously valued your advice and deep commitment to public service and will miss working with you in government.”
In an incendiary letter, Mr Javid said the British people “expect integrity from their government” but voters now believed Mr Johnson’s administration was neither competent nor “acting in the national interest”.
Mr Johnson faced more resignations as three more MPs quit his government in the wake of the shock resignations from Mr Sunak and Mr Javid.
Jonathan Gullis, described as a Johnson “ultra-loyalist”, resigned his role as parliamentary private secretary to the Secretary of State for Northern Ireland, saying the Conservative Party has been “more focused on dealing with our reputational damage rather than delivering for the people of this country”.
Conservative MP Saqib Bhatti quit his role as parliamentary private secretary to the health secretary, stating “recent events have undermined trust and standards in public life”.
MP Nicola Richards resigned saying: “I will always remain loyal to my constituents and the Conservative Party. Tonight I’ve made the tough decision to resign as a PPS.”
Virginia Crosbie has quit her role as parliamentary private secretary at the Welsh Office, stating she “cannot continue to defend” the Prime Minister’s actions.
Posting her resignation on Facebook, the Ynys Mon MP wrote: “I am forced to say that the sheer number of allegations of impropriety and illegality -many of them centred around Downing St and your premiership- is simply making your position untenable.”
MP Theo Clarke resigned as trade envoy to Kenya, saying she was “shocked” to see her colleagues defending the Government with “assurances that turned out to be false”.
The resignations came as Mr Johnson was forced into a humiliating apology over his handling of the Chris Pincher row after it emerged he had forgotten about being told of previous allegations of “inappropriate” conduct.
Mr Pincher quit as deputy chief whip last week following claims that he groped two men at a private members’ club, but Mr Johnson was told about allegations against him as far back as 2019.
The Prime Minister acknowledged he should have sacked Mr Pincher when he was told about the claims against him when he was a Foreign Office minister in 2019, but instead Mr Johnson went on to appoint him to other government roles.
Asked if that was an error, Mr Johnson said: “I think it was a mistake and I apologise for it. In hindsight it was the wrong thing to do.
“I apologise to everybody who has been badly affected by it. I want to make absolutely clear that there’s no place in this Government for anybody who is predatory or who abuses their position of power.”
Mr Sunak said he had “reluctantly come to the decision that we cannot continue like this”.
In his letter to the PM, he wrote: “The public rightly expect government to be conducted properly, competently and seriously. I recognise this may be my last ministerial job, but I believe these standards are worth fighting for and that is why I am resigning.”
In his letter to the PM, Mr Javid told the PM that the “tone you set as a leader, and the values you represent, reflect on your colleagues, your party and ultimately the country.”
He said the Tory party “may not have always been popular, but we have been competent in acting in the national interest.
“Sadly, in the current circumstances, the public are concluding that we are now neither.”
He added: “The country needs a strong and principled Conservative Party, and the party is bigger than any one individual. I served loyally and as a friend, but we all serve the country first. When made to choose between those loyalties there can only be one answer.”
Mr Johnson wrote back saying Mr Javid had served the Government and the people of the United Kingdom with “distinction”.
“You will be greatly missed, and I look forward to your contribution from the backbenches,” he wrote.
The Labour leader Sir Keir Starmer said Mr Johnson’s Government was now “collapsing”.
He said: “After all the sleaze, the scandals and the failure, it’s clear that this Government is now collapsing. Tory cabinet ministers have known all along who this Prime Minister is.
“They have been his cheerleaders throughout this sorry saga: backing him when he broke the law, backing him when he lied repeatedly, backing him when he mocked the sacrifices of the British people.
“In doing so, they have been complicit every step of the way as he has disgraced his office and let down his country.
“If they had a shred of integrity they would have gone months ago. The British public will not be fooled.
“The Tory party is corrupted and changing one man won’t fix that. Only a real change of government can give Britain the fresh start it needs.”
In another significant blow to the Prime Minister, the former Brexit Minister and close ally of Mr Johnson Lord Frost tweeted his support for Mr Sunak and Mr Javid.
He said: “In short, Rishi Sunak and Sajid Javid have done the right thing.
“It gives me no pleasure to say it and I had hoped events might have taken a different course but I’m afraid the developments of the last week show there is no chance of the Prime Minister either putting in place the necessary change of approach to running a Government or establishing a new policy direction…
“Accordingly and with sadness I believe in the interests of the country…our new found self government and the Conservative Party would be best served by new leadership and a new Prime Minister.”
Liberal Democrats leader Sir Ed Davey added to the pressure on Mr Johnson to quit, saying in a statement: “Boris Johnson has got to go, his Government of chaos has failed our country.”