Rishi Sunak has vowed to fix Liz Truss's "mistakes" and warned of "difficult decisions to come" as he seeks to resolve the economic turmoil.
The new Prime Minister said the county was facing a "profound economic crisis" after the pandemic and the war in Ukraine and he would put stability at the heart of his premiership.
In his first speech outside Downing Street, Mr Sunak said he would put "economic stability" at the heart of his premiership and hinted at looming cuts to public spending as the Government seeks to steady the ship.
He paid tribute to Liz Truss for her "restlessness to create change" but made it clear he was ripping up her plans.
He said: "Some mistakes were made, not born of ill will or bad intentions, quite the opposite in fact. But mistakes none the less."
In a swipe at his rival Boris Johnson, he pledged that his Government will have "integrity, professionalism and accountability at every level."
He went on: "Trust is earned and I will earn yours."
Mr Sunak was crowned as the new Conservative leader yesterday without a vote after his rivals Penny Mordaunt and Boris Johnson dropped out of the race.
He faces an uphill battle to reunite warring Tories and stabilise the country after crisis-hit Liz Truss's 49-day stint in office.
Ms Truss tendered her resignation to King Charles at Buckingham Palace this morning and Mr Sunak was formally confirmed as the UK's 57th Prime Minister by the monarch.
It marks an extraordinary shift from the start of September, when Ms Truss trounced him in the Tory leadership race and left her rival in the political wilderness.
But her disastrous tax-cutting plans triggered a wave of economic and political turmoil, leading to her resignation last week.
The new Prime Minister will now turn his attention to shaping his top team, with a Cabinet reshuffle expected to kick off this afternoon.
Long-time backers Dominic Raab, Commons Treasury Committee chairman Mel Stride and ex-chief whip Mark Harper have been tipped for senior roles.
Jeremy Hunt, who replaced Kwasi Kwarteng as Chancellor, is expected to remain in post. He is working urgently on a fiscal plan to steady the economic turmoil, due to be held on October 31.
Ms Truss threw down the gauntlet to Mr Sunak in a bizarre final speech today where she urged him to be "bold" and pointedly mentioned cutting taxes and defence spending.
In a three minute address outside No10, an unrepentant Ms Truss failed to apologise for her disastrous record and instead quoted Roman philosopher Seneca: “It is not because things are difficult that we do not dare, it is because we do not dare that they are difficult."
Boris Johnson finally offered his "congratulations" to the new PM, adding that "on this historic day, this is the moment for every Conservative to give our new PM their full and wholehearted support".
