He received a flurry of messages from leaders around the world. Here is a selection of the reactions:
Zelenskyy wants strong partnership
Ukrainian President Volodymyr Zelenskyy wrote on Twitter that he hoped Sunak would be able “to successfully overcome all the challenges facing British society and the whole world today”.
He said he was “ready to continue strengthening the Ukrainian-British strategic partnership”, with the UK one of Kyiv’s staunchest supporters against Russia’s invasion.
Congratulations to @RishiSunak on taking office as 🇬🇧 Prime Minister! I wish you to successfully overcome all the challenges facing British society and the whole world today. I’m ready to continue strengthening the 🇺🇦-🇬🇧 strategic partnership together!
— Володимир Зеленський (@ZelenskyyUa) October 25, 2022
‘Tackling challenges’ with France
French President Emmanuel Macron tweeted that “together we will continue working to tackle the challenges of the moment, including the war in Ukraine and its many consequences for Europe and the world”.
Italy ‘eager’ to cooperate
From Italy, newly-installed Prime Minister Giorgia Meloni said she was “eager to cooperate with [Sunak] and his cabinet on the common challenges, standing for our shared values of freedom and democracy”.
‘Close friends’ with Germany
“I look forward to our further cooperation and partnership in NATO and [the] G7 as close friends,” German Chancellor Olaf Scholz tweeted.
‘Positive EU-UK relations’
Maros Sefcovic, the European Union’s point man on post-Brexit ties with the UK, said “a positive EU-UK relationship is of strategic importance”.
He pledged to work towards “a partnership in full respect of our agreements”, including the contentious issue of Northern Ireland’s land border with EU member Ireland.
European Commission chief Ursula von der Leyen said, “In these testing times for our continent, we count on a strong relationship with the UK to defend our common values.”
Russia sees no hope for improvement
Kremlin spokesman Dmitry Peskov said in Moscow, “we do not see any preconditions, grounds, or hope that in the foreseeable future there will be any positive changes” in the relationship between the UK and Russia.
Biden welcomes ‘groundbreaking’ PM
Even before Sunak’s appointment as prime minister by King Charles III – the monarch’s first new government chief since taking over from his mother Elizabeth II – US President Joe Biden said it was “groundbreaking” that the UK would be led by a person with Indian heritage.
“It’s pretty astounding, a groundbreaking milestone and it matters,” Biden said at a White House celebration of the Indian Diwali festival, celebrated on Monday.
Special Diwali wishes from Modi
Indian Prime Minister Narendra Modi did not wait for Sunak to be officially appointed, sending congratulations via Twitter on Monday.
“As you become UK PM, I look forward to working closely together on global issues,” Modi wrote. “Special Diwali wishes to the ‘living bridge’ of UK Indians, as we transform our historic ties into a modern partnership,” he added.
Sunak is married to an Indian, Akshata Murty, the daughter of the co-founder of IT giant Infosys.
Warmest congratulations @RishiSunak! As you become UK PM, I look forward to working closely together on global issues, and implementing Roadmap 2030. Special Diwali wishes to the 'living bridge' of UK Indians, as we transform our historic ties into a modern partnership.
— Narendra Modi (@narendramodi) October 24, 2022
Poland wishes ‘success’
Polish President Andrzej Duda wrote that he was “looking forward to our meeting and cooperation and wish you success in your endeavours”.
“Poland and the UK are steadfast allies and are standing together against the Russian invasion of Ukraine,” he added.
‘Strengthening ties’ with Spain
Spanish Prime Minister Pedro Sanchez said, “We will continue to strengthen our ties for the benefit of our fellow citizens. Only solidarity and unity will allow us to confront the challenges and consequences of the war in Ukraine.”
Canada looks forward to collaboration
Prime Minister Justin Trudeau said in a statement that he looks forward to working with Sunak to strengthen Canada-UK relations “as we continue to address ongoing global concerns, including Russia’s illegal and unjustifiable invasion of Ukraine, economic uncertainty, and climate change”.
“I also look forward to collaborating with Prime Minister Sunak to bolster our important economic relationship as we negotiate a comprehensive, ambitious, and inclusive Canada-United Kingdom Free Trade Agreement, as well the UK’s accession to the Comprehensive and Progressive Agreement for Trans-Pacific Partnership,” Trudeau said.
Nigeria welcomes ‘milestones’
Nigerian President Muhammadu Buhari said with Sunak “as the first Prime Minister of British-Asian descent and the youngest in about 200 years, these milestones will be especially inspiring for young people” in the Commonwealth, the association mostly of former British colonies.
“We seek to deepen our partnership with Britain” to address challenges, including “terrorism”, food insecurity, energy and climate change, Buhari added.