Sajid Javid appointed UK Home Secretary after Amber Rudd resignation
Javid, a former investment banker, will leave his role as Communities, Local Government and Housing Secretary, to take one of the most powerful seats in UK politics.
Rudd's resignation was a resounding blow to the government as it faces public outrage over the targeting of the so-called Windrush generation of migrants.
Rudd faced intensifying pressure over the treatment of elderly Commonwealth citizens primarily from the Caribbean, and told lawmakers last week that there were no targets for the removal of people deemed to be in the country illegally.
But she tendered her resignation after leaked documents addressed to her office showed that such goals were in place.
"I should have been aware of this, and I take full responsibility for the fact that I was not," she said in her resignation letter to Prime Minister Theresa May, conceding that she "inadvertently misled the Home Affairs Select Committee".
Rudd's dramatic exit comes as a severe setback for May, who publicly declared her "full confidence" in Rudd as recently as Friday and faces potentially bruising local council elections across England on Thursday.
The government has faced mounting controversy after it emergedmany from the Windrush generation, who had been living in the UK legally since the Second World War, had their benefits cut, denied medical treatment and threatened with deportation.
Their treatment stemmed from a "hostile environment" immigration policy pioneered by May when she was home secretary between 2010 and 2016, and then continued by Rudd.
Many have also been calling for the resignation of the Prime Minister, the "architect" of the hostile immigration policy, who has weathered a series of cabinet resignations over her tenure.
The opposition Labour Party, who had been calling for Rudd's resignation for weeks, accused the Home Secretary of incompetence and of being a "human shield" for May.
"This was inevitable, the only surprise is that it took so long," said shadow interior minister Diane Abbott following Rudd's resignation.
"The architect of this crisis, Theresa May, must now step forward to give a full and honest account of how this inexcusable situation happened on her watch."
"Many of the elements of this hostile environment originated under Theresa May and, most important of all, it was in 2014 that she passed legislation which removed the protection from deportation which up until then had applied to Commonwealth citizens," Abbot told BBC's Radio 4.
In a written response to Rudd's resignation, May said she believed the minister had given her testimony "in good faith" and said the country was trying to enforce a "firm but fair" immigration policy.
The loss of a key minister comes at a delicate time for May, who could see the Tories wiped out in London at the local elections, with several once-safe Conservative councils potentially flipping to Labour.
Rudd, who very narrowly retained her seat as MP for Hastings on England's south coast during last year's snap election, had led the Home Office since 2016. Rudd was also seen as a moderate on the European Union and a balancing force in a cabinet made up of several big-name pro-Brexit figures.
Foreign Secretary Boris Johnson and Environment Secretary Michael Gove, who were at the forefront of the campaign for Britain to leave the EU, were quick to praise their colleague on social media following news of the resignation.
"Really sad to lose @AmberRuddHR from Cabinet. A fine colleague who did a great job during last year's terrorist attacks and cares deeply about the people she serves," Johnson tweeted.
One of the more heartfelt reactions came from George Osborne, long-time finance minister under former Prime Minister David Cameron.
He wrote: "The Government just got a bit less human."
Opponents however have ridiculed the former investment banker and one-time "aristocracy co-ordinator" where she sourced upper class extras for films such as Four Weddings and A Funeral, for her lack of compassion in regard to immigration issues.
Rudd had been due to make another appearance before parliament on Monday, but instead opted to resign late Sunday.
In her resignation letter, she admitted that sometimes people with a legal right to be in Britain had not been treated "fairly and humanely", adding that she had hoped to push through new legislation in the coming months to protect the Windrush generation.
In 1948, the ship Windrush brought the first group of migrants from the West Indies to help rebuild post-war Britain, and many others followed from around the Commonwealth.
They were given a legal right to remain by a 1971 law, but many never formalised their status, often because they were children who came over on their parents' or siblings' passports and then never applied for their own.
A sticking point of the scandal was the fact that the Home Office, under the leadership of Theresa May in 2010, destroyed thousands of Windrush arrivals' landing cards, which recorded their arrival to the UK, and has left them without immigration documents.
In recent years a government clampdown on illegal immigration has begun to identify those without papers - scooping up many elderly people from the Windrush generation.
Outrage over the plight of Windrush migrants - some of whom have lost jobs and fallen into debt as they struggled to prove their status - led to a personal apology from Prime Minister Theresa May to Caribbean leaders in April.