The Prime Minister jets off to Bali, Indonesia, on Sunday to join other leaders of the world’s biggest economies including US President Joe Biden, France’s Emmanuel Macron and China’s Xi Jinping.
Russia’s Vladimir Putin is expected to skip the event and send the country’s Foreign Minister Sergei Lavrov in his place instead.
The annual G20 leaders’ gatherings began in response to the 2008 financial crisis, establishing the summit as the main global forum for economic cooperation.
But Mr Sunak said this year’s meeting will not be "business as usual" as the world confronts the most significant set of economic challenges since then.
In a statement ahead of his departure, Mr Sunak said: "Putin’s war has caused devastation around the world - destroying lives and plunging the international economy into turmoil.
"This G20 summit will not be business as usual. We will call out Putin’s regime, and lay bare their utter contempt for the kind of international cooperation and respect for sovereignty forums like the G20 represent.
"In clear contrast to Putin’s disruption, the UK and our allies will work together to make meaningful progress solving the economic challenges we face and making lives better for our people."
Mr Sunak is expected to confront Mr Lavrov in a speech during the first plenary session on Tuesday.
Russia’s top diplomat is prone to walk out when challenged over the invasion, doing so at a G20 foreign ministers’ meeting in July.
The summit comes after Russia withdrew from the strategic city of Kherson in what the UK government has called “another strategic failure” for Putin’s troops.
Ukrainians across the country have reacted with jubilation to scenes of Ukrainian troops entering the southern port city.
Kherson had been the only provincial capital claimed by Russian forces since the invasion began in late February.
Due to supply issues, however, Russian officials announced a withdrawal from the west bank of the Dnipro River during the week.
The withdrawal was completed in the early hours of Friday, in what UK officials said had brought “significant reputational damage” to Russia.
Ukraine’s president Volodymyr Zelensky declared it as a “historic day” for the country in an address to the nation, as crowds celebrated in central Kyiv and elsewhere.
“The people of Kherson were waiting. They never gave up on Ukraine. Hope for Ukraine is always justified - and Ukraine always regains its own,” he said.
The G20 summit is the first since Russia’s invasion of Ukraine, and will likely be dominated by the fallout from the conflict, which has driven up energy and food prices worldwide.
Finding consensus will be difficult as the group encompasses geopolitical rivals such as the US and China.
With divisions deepened by the Ukraine war, there is uncertainty over whether leaders will be able to agree a traditional joint statement at the end of the Bali summit.
The Indonesian hosts are understood to have scrapped the official family photo as some leaders will be reluctant to be pictured with Russia’s representative.
The summit is one of Mr Sunak’s first outings on the world stage as leader, after his flying visit to Egypt for COP27 climate talks.
He will return to the UK on Thursday just in time for the highly anticipated autumn budget, in which Chancellor Jeremy Hunt could impose up to £60 billion in tax rises and spending cuts.