Jens Stoltenberg, the Nato Secretary General, declared Ukraine would be invited to join Nato as the bloc looks to shore up its ally in the war it is fighting with Russia for control of its territory.
Mr Stoltenberg said the allies had decided on Tuesday to move beyond the position, adopted at a 2008 summit, that Ukraine could apply for membership. The 31-member alliance backed a proposal that stated an invite would be issued to Ukraine.
The decision was part of a three-point accelerated path to membership that will include the inaugural meeting of the Nato-Ukraine Council in Vilnius on Wednesday.
Ukraine's military is to be brought into the alliance in a process involving increased support from western allies.
Nato leaders will commit to offering more military support to ensure the country regains territory in the war with Russia, in turn boosting its integration with western forces, Mr Stoltenberg said.
Ukrainian President Volodymyr Zelenskyy landed in Vilnius on Tuesday afternoon, hours after he published a warning on Twitter that unexpected conditions were being added during negotiations. These could show division, which would only encourage Russian aggression, he said. "Uncertainty is weakness," he wrote. "And I will openly discuss this at the summit."
Mr Zelenskyy later declared on Twitter he was grateful for new offers of support and would continue talks with counterparts on Thursday.
Ukrainian officials had wanted a timetable but Mr Stoltenberg said there had never been any timetables for a Nato accession.
"If you look at other membership processes, there has not been a timeline," he said, adding that the two-step process of issuing an invite followed by a conditions-based membership action plan had be cut to one. "We wish to issue an invite to Ukraine to join when conditions are met. What we are saying in the communique is that Nato has moved beyond a membership action plan."
Kaja Kallas, the Estonian Prime Minister, said there was a common understanding that Ukraine could not join Nato while the war with Russia was still being fought. She added, however, that it should only be a "short track" to Kyiv's accession thereafter.
"We understand that it can't happen while the war is going on, and nobody's really demanding that, not even the Ukrainians, but we have to make sure that when all the conditions are met and we have the opportunity window when the war is over, then we can do this fast," she said.
"It is very important that, you know, the assurances that the [Nato] countries give are very practical."
"What it really means ... is that the West is behind Ukraine."
French President Emmanuel Macron and German Chancellor Olaf Scholz were the first leaders at the summit to announce further significant weapons packages aimed to give Ukraine's armed forces more punch on the battlefield.
"I have decided to increase deliveries of weapons and equipment to enable the Ukrainians to have the capacity to strike deeply," Mr Macron said.
Britain said in May that it was supplying the Storm Shadow, a Franco-British surface-to-air missile produced by MBDA. Its French version, known as Scalp, has a range of about 250km.
Mr Macron said the delivery would adhere to France's policy of assisting Ukraine in defending its territory, implying that Paris had received assurances from Kyiv that the missiles would not be fired into Russia.
Germany's new aid package, valued at nearly €700 million ($769 million), includes two Patriot missile system launchers, 40 Marder infantry fighting vehicles and 25 Leopard 1 tanks, as well as 20,000 artillery rounds and 5,000 rounds of smoke ammunition.
British Prime Minister Rishi Sunak confirmed an eight-fold increase in the UK’s production capacity of 155mm artillery ammunition under a new £190 million contract.