Leaders are expected to endorse the EU executive's recommendations for Ukraine and neighbouring Moldova, announced on Friday, at a summit next week.
Ukrainian President Volodymyr Zelenskiy tweeted that the bravery of Ukrainians had created the opportunity for Europe to "create a new history of freedom, and finally remove the grey zone in Eastern Europe between the EU and Russia".
In his nightly address on national television, Zelenskiy said the decision of the EU member states remained to be seen, but added: "You can only imagine truly powerful European strength, European independence and European development with Ukraine."
European Commission President Ursula von der Leyen announced the executive's decision while dressed in Ukrainian colours - a yellow blazer over a blue blouse.
"Ukrainians are ready to die for the European perspective," she said. "We want them to live with us the European dream."
Russian President Vladimir Putin railed at the West in a grievance-filled speech in St Petersburg on Friday, but sought to play down the EU issue.
"We have nothing against it," he said. "It is not a military bloc. It's the right of any country to join economic union."
However, Kremlin spokesman Dmitry Peskov said Russia was closely following Ukraine's EU bid, especially in the light of increased defence co-operation among the 27-member bloc.
Ukraine applied to join the EU four days after Russian troops poured across its border in late February.
It was joined days later by Moldova and Georgia - smaller ex-Soviet states also contending with separatist regions backed by Russia.
Though only the start of a process that may take many years and require extensive reforms, the European Commission move puts Kyiv on course to realise an aspiration out of reach just months ago.
One of Putin's stated objectives in launching an invasion that has killed thousands of people, destroyed cities and driven millions to flee was to halt the West's eastward expansion via the NATO military alliance.
Friday's announcement underlined how the war has had the opposite effect: convincing Finland and Sweden to join NATO, and now the EU to embark on potentially its most ambitious expansion since welcoming eastern European states after the Cold War.
In his speech, Putin denounced the United States for considering itself "God's emissary on earth" and said Western intransigence had given Russia no choice but to launch its "special military operation" in Ukraine.
He also questioned whether it was "advisable" for the EU to let Ukraine join, saying Kyiv would need huge economic subsidies other members may not be willing to give.
Adding fuel to the global showdown, Russian media broadcast images of what they said were two Americans captured while fighting for Ukraine.
EU membership is not guaranteed - talks have been stalled for years with Turkey, a candidate since 1999. If admitted, Ukraine would be the EU's largest country by area and its fifth most populous.
Ukraine and Moldova are far poorer than current EU members and have recent histories of volatile politics, organised crime and conflicts with Russian-backed separatists.
But in 44-year-old Zelenskiy, and Maia Sandu, 50, they have pro-Western leaders who came of age outside the Soviet Union.
The latest foreign dignitary to visit Kyiv was British Prime Minister Boris Johnson, who on Friday offered training for Ukrainian forces and said Britain would stand by the Ukrainian people "until you ultimately prevail".
Within Ukraine, Russian forces have used their artillery advantage to blast their way into cities in the eastern Donbas region in a punishing attritional phase of the war.
Ukrainian officials said troops were still holding out in Sievierodonetsk, in neighbouring Luhansk province and scene of the worst recent fighting, but it was impossible to evacuate more than 500 civilians trapped in a chemical plant due to shelling and heavy fighting.
In the south, Ukraine has mounted a counteroffensive and claims to have made inroads into territory seized by Russia.
