Keir Starmer will become the first PM since Theresa May to hold face-to-face talks with the Chinese Premier.
He will meet Xi Jinping at the G20 summit as world leaders descend on Rio de Janeiro in Brazil on Tuesday. Mr Starmer told reporters that he will be having a "serious" discussion with Xi - but refused to say what they would talk about.
It comes at a time of heightened tensions between the UK and Beijing, with no meeting held between leaders since 2018. Labour has previously suggested the Chinese government is committing genocide of Uyghur Muslims.
Mr Starmer said: "We are both global players, global powers, both permanent members of the security council and of the G20. China’s economy is obviously the second biggest in the world. It’s one of our biggest trading partners and therefore I will be having serious, pragmatic discussions with the president when I meet him."
The summit comes amid growing unease about Donald Trump's impending return to the White House. Mr Trump and his allies have indicated they could withdraw from key environmental agreements and withdraw support from Ukraine.
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There is also nervousness that the Trump administration could open up trade wars by bringing in restrictive tariffs.
Mr Starmer said he intends to make sure the UK's relationship with the US is "as strong going forward as it's ever been". The President-elect has said he wants to withdraw from the landmark Paris Agreement on climate change.
And Argentine President Javier Milei, a key ally of Mr Trump, has also signalled he will pull out. Asked if this is a death knell in the fight against climate change, Mr Starmer said: “No, I don't think so.
"Amongst the reasons I went to (the Cop29 summit) last week was because I think it's important for the UK to show leadership on an important issue.
And in a veiled swipe at the two leaders he said tackling climate change is an "obligation, which is on all of us to play our part".
He told reporters he will not rule out giving Mr Trump a state visit once he takes office. The PM said: "Obviously, I've had a constructive meeting with President elect Trump a few weeks ago, constructive discussion with him on the phone the other day.
"But I'm not going to get ahead of things." The G20 will bring together the 19 countries with the largest economies in the world.