Although it could take Ukraine and neighbouring Moldova more than a decade to qualify for membership, the decision at a two-day EU summit is a symbolic step that signals the bloc's intention to reach deep into the former Soviet Union.
"A historic moment," European Council chief Charles Michel tweeted.
"Today marks a crucial step on your path towards the EU," he said, adding: "Our future is together."
The move, in which Moldova was also granted candidate status, kick-starts the EU's most ambitious expansion since it welcomed eastern European countries after the Cold War.
"All the people in Ukraine are watching and waiting for this decision," said Ivan Zichenko, a 34-year-old Ukrainian from the devastated city of Kharkiv, who now lives in Brussels.
"It's very, very important to raise their morale," he said as a few dozen people chanted "Ukraine is Europe" at a rally outside the Brussels building where EU leaders were meeting.
Behind the triumphant rhetoric, however, there is concern within the EU about how the bloc can remain coherent as it continues to enlarge.
After starting in 1951 as an organisation of six countries to regulate industrial production, the EU now has 27 members that face complex challenges from climate change and the rise of China to a war on their own doorstep.
Russian President Vladimir Putin says his "special military operation" launched in Ukraine in late February was partly necessitated by NATO encroachment into what Russia characterises as its rightful geographical sphere of influence.
The EU's green light "is a signal to Moscow that Ukraine, and also other countries from the former Soviet Union, cannot belong to the Russian spheres of influence," Ukraine's EU ambassador Chentsov Vsevolod told Reuters earlier on Thursday.
"There are Ukrainian soldiers calling home from the front line and asking: what is happening with our candidate status? It's amazing how important it is for Ukrainian people."
While Ukraine and Moldova were expected to be welcomed into the EU's waiting room, Georgia was given "a European perspective" but told it must fulfil conditions before winning candidate status.
Reticence over EU enlargement has slowed progress towards membership for a group of Balkans countries - Albania, Bosnia, Kosovo, Montenegro, North Macedonia and Serbia - whose leaders met their EU counterparts in Brussels on Thursday morning.
Albanian Prime Minister Edi Rama said as he arrived at a meeting with EU leaders ahead of the bloc's summit: "Welcome to Ukraine, it's a good thing to give candidate status but I hope the Ukrainian people will not have much illusions about this."
A draft of the summit statement showed that EU leaders will again give "full and unequivocal commitment to the EU membership perspective of the Western Balkans".
But Ukraine's fast track to formal candidate status has only served to increase their feeling of being sidelined, which carries the risk for the EU that Russia and China extend their influence into the Balkan region.
