On the most important day of his four-day visit to China, the first by a British prime minister in eight years, Starmer held talks with Xi at the Great Hall of the People before they lunched together.
Starmer, whose centre-left Labour Party government has struggled to deliver the growth it promised, has made improving relations with the world's second largest economy a priority, despite lingering misgivings about espionage and human rights.
"China is a vital player on the global stage, and it's vital that we build a more sophisticated relationship where we can identify opportunities to collaborate, but of course, also allow a meaningful dialogue on areas where we disagree," Starmer told Xi at the start of their meeting.
Xi said ties with Britain had gone through "twists and turns" that did not serve the interests of either country and that China stood ready to develop a long-term strategic partnership.
Starmer is the latest Western leader to engage in a flurry of diplomacy with China, as nations hedge against unpredictability from the United States under President Donald Trump.
Trump's on-off threats of trade tariffs and pledges to grab control of Greenland, an autonomous territory of Denmark, have rankled longstanding allies like Britain.
Starmer's visit immediately follows that of Canadian Prime Minister Mark Carney, who signed an economic deal with Beijing to tear down trade barriers, drawing Trump's ire.
Kerry Brown, professor of Chinese studies at King's College London, said he expected that a number of deals between Britain and China would be announced to show how their relationship has improved.
"This must look like it's been a success," he said. "For both sides, they don't want a meeting which is going to be arguing about things they disagree on."
Starmer has adopted a new policy of engagement with China after ties deteriorated for years under previous Conservative governments, when London curbed some Chinese investment over national security worries and expressed concern over a crackdown on political freedoms in Hong Kong.
"I made the promise 18 months ago, when we were elected into government, that I would make Britain face outwards again," Starmer told Xi. "Because, as we all know, events abroad affect everything that happens back in our home countries, to prices on the supermarket shelves to how secure we feel."
Kemi Badenoch, the leader of Britain's opposition Conservative Party, said she would not have gone to China because of the security risks the country poses.
British security services have said China routinely spies on the government. China has denied the claims.
