Prime Minister Sir Keir Starmer is expected to discuss European security and the likely impact of a second Trump presidency when he holds talks with French President Emmanuel Macron in Paris on Monday.
Ahead of attending a ceremony at the Tomb of the Unknown Soldier, Macron and Starmer are expected to discuss Russia's ongoing invasion and the humanitarian situation in Gaza, Downing Street said.
Their meeting comes as questions are being asked about US President-elect Donald Trump's support for Ukraine after he said he could end the war with Russia "in one day".
Trade will also be on the agenda, with Trump saying he will impose a blanket 20% tariff on imports into the US.
Sir Keir - who is believed to be the first British leader to attend the ceremony on the Champs Elysee since Winston Churchill in 1944 - will also meet French Prime Minister Michel Barnier.
Questions have been raised following Trump's US presidential election victory about what his second term could mean for US support for Ukraine and Nato.
Over the weekend, the Washington Post reported Trump has already spoken to Vladimir Putin - urging the Russian leader not to further escalate the war.
UK Defence Secretary John Healey said if the reports of the call were correct "then President Trump is exactly right to warn Putin against escalation in Ukraine".
Speaking to BBC Breakfast, he said he expected the United States to "remain steadfast" in its support of Ukraine due to the strength of "bipartisan support" in the country.
"We have stepped up our support of Ukraine, we’re speeded up the delivery of aid, and we’re spending more now on Ukraine and supporting Ukraine than we ever have done before," he added.
The UK and France have said backing Ukraine against Russia is essential when it comes to to protecting the European continent as a whole.
Trump has previously told Nato members to increase defence spending, saying he would let aggressors such as Russia do "whatever the hell it wants" to those that do not.
During his election campaign, Donald Trump declined to specify how he would end the war between Russia and Ukraine in a day - but it could involve imposing a deal on both sides.
Bryan Lanza, who worked on Trump's 2024 presidential campaign, told the BBC that Ukrainian President Volodymyr Zelensky had to have a "realistic vision for peace", which would not involve ending the Russian annexation of Crimea.
However, a spokesperson for Donald Trump distanced him from the remarks, saying Mr Bryan "does not speak for him".
The Armistice Day meeting between Starmer and Macron comes as fighting between the two sides intensifies.
Exchanges at the weekend saw the largest drone attacks by both sides against each other since the start of the war, and Russia's defence ministry said it intercepted 84 Ukrainian drones over six regions, including some approaching Moscow.
On Sunday, Treasury Minister Darren Jones told BBC One's Sunday with Laura Kuenssberg programme that the government wanted to increase defence spending from 2.3% to 2.5% of the national income.
However, he did not say when the target would be reached or whether it would be met before the next election, which could be held in 2029, at the latest.
Sir Keir joined other political leaders and members of the Royal Family, including the Prince and Princess of Wales, for the annual National Service of Remembrance ceremony at the Cenotaph in London on Sunday.
King Charles led the nation in two minutes of silence in remembrance of those who lost their lives serving in the two world wars or other conflicts.
As on Remembrance Sunday, two minutes of silence will be held on Armistice Day at 11:00 GMT.
It marks the moment World War One ended, at 11:00 on the 11th day of the 11th month, in 1918.
