Sir Keir Starmer is expected to accuse Russian President Vladimir Putin of "hollow promises" in ceasefire talks at the summit in Paris.
The British Prime Minister will attend the meeting of the so-called "coalition of the willing" after Emmanuel Macron suggested a European peacekeeping force could "respond" if attacked by Russia.
Sir Keir will present the outcomes of a series of defence talks in London where officials were drawing up a strategy to support Kyiv and deter future aggression from Moscow.
More than 200 military planners from countries across the world met to consider in detail the structure of any future deployment, including proposals for air, sea and land forces.
Number 10 said the Prime Minister will tell allies that "excellent progress" was made and Europe is "mobilising together in pursuit of peace, but now we must keep up the momentum".
He will also accuse the Russian president of "playing games" with an agreement for a naval ceasefire in the Black Sea after separate talks between US negotiators and their counterparts in Kyiv and Moscow.
Russia and Ukraine have accused each other of breaking the terms of a tentative US-brokered deal to pause strikes on energy infrastructure, underscoring the challenges in negotiating a broader peace.
On Tuesday it was announced that Ukraine and Russia had agreed to paused hostilities in the Black Sea.
