The 42-year-old MP had been elected to the post by the Conservative Party on Monday, 24 October, after being backed my a majority of his party's colleagues.
Newspapers from the United Kingdom carried front-page banner headlines displaying Sunak's rise to power, with some praising the Indian-origin leader, and others taking a slightly harsher approach towards him.
Here are a few banner headlines of popular British newspapers on Tuesday, 25 October:
From 'A New Dawn' To 'Who Elected You?': How British Media Reacted to Sunak
The Daily Mail called Sunak's victory a "a new dawn for Britain".
This comes in the backdrop of weeks of turmoil that had plagued the country and the Conservative Party - following decisions taken by the Liz Truss-led government which had led to economic instability and worsened the cost-of-living crisis even further.
The newspaper further added: "After weeks of turmoil, Tory party fightback starts here".
The Daily Mirror, on the other hand, took a more critical approach, asking, "Who voted for you?" and calling Sunak "Our new (unelected) PM".
It adds that yet another Tory leader has become the country's leader without winning a single vote from the electorate.
"Richer than the king and clueless about ordinary people, he is intent on eye-watering cuts," the newspaper added.
The Guardian's front page on Tuesday was headlined: "Unite or die – Sunak’s warning to Tory MPs".
The newspaper's deputy political editor also highlighted the fact that Sunak had promised to "end Conservative psychodrama" and "prioritise policies, not personalities".
Meanwhile, The Sun took a lighter approach to events, showcasing Sunak holding a lightsaber, of Star Wars fame, and having a headline which read, "The force is with you, Rishi".
Metro also went down the lighter route, saying, "Here comes the Sunak" on its front-page, referencing the popular hit of The Beatles, called "Here Comes the Sun".