Ms Truss will tell a recovery conference in Switzerland on Monday that the UK will “do everything possible to ensure Ukraine wins the war and recovers”.
Ukrainian President Volodymyr Zelenskyy has asked the UK to champion the recovery of the capital of Kyiv and the surrounding region, the British Foreign Office said.
But attempts to recover and rebuild are made more challenging by Russia’s ability to strike the capital with missiles as its forces make creeping advances in the east.
Ms Truss will use the conference in the city of Lugano to set out a vision to give immediate support and long-term commitments to work alongside the Ukrainians.
“Ukraine’s recovery from Russia’s war of aggression will be a symbol of the power of democracy over autocracy," say excerpts of her address, which were released early.
"It will show [Russian President Vladimir] Putin that his attempts to destroy Ukraine have only produced a stronger, more prosperous and more united nation.
“We have led on support for Ukraine during the war and will continue to lead in supporting the Ukrainian government’s reconstruction and development plan.”
Ms Truss will announce plans to host next year’s recovery conference as the government commits to a Marshall Plan-style programme, similar to the one used to rebuild Europe after the Second World War.
“The UK will do everything possible to ensure Ukraine wins the war and recovers. We need to be in this for the long haul,” she is expected to say.
Mr Putin has focused his assault on the eastern regions of Luhansk and Donetsk after withdrawing from the offensive in Kyiv amid fierce resistance.
Moscow claims that Russian forces have taken control of Lysychansk, the last major Ukrainian-held city in Luhansk.
Russia hit Kyiv with missile strikes last week in what Ukrainians called an intimidation attempt as they seek a return to normal life while still under siege.
Authorities said at least 19 people, including two children, were killed in a missile attack on the town of Serhiivka, near Odesa, on Friday.
Another 19 were killed and 62 injured in a missile strike on a shopping centre in the central city of Kremenchuk last Monday, Ukrainian authorities said.