Speaking via video link from Ukraine, Zelensky renewed his call for continued Western support for Kyiv in its fight against Moscow's ongoing invasion.
He thanked the EU for its steadfast assistance and appealed for additional support as winter approaches, amid escalating Russian attacks on Ukrainian infrastructure.
Zelensky's address was met with prolonged applause from MEPs, as European leaders debated future strategies to bolster Ukraine’s security, news outlets reported.
Zelensky also told MEPs that the number of North Korean troops stationed inside Russia could grow to 100,000, the Reuters news agency reported.
It noted that Kyiv and its Western allies have accused North Korea of supplying Russia with weaponry and troops to support its full-scale invasion of Ukraine.
"Now, Putin has brought 11,000 North Korean troops to Ukraine's borders," Zelensky told the European Parliament.
"This contingent may grow to 100,000," he added, as cited by Reuters.
In a separate speech to the Ukrainian parliament later in the day, Zelensky reaffirmed Ukraine's commitment to defending its sovereignty and territorial integrity, Ukrainian state news agency Ukrinform reported.
"We are not trading Ukraine's sovereignty, security, or future," he declared, as quoted by Ukrinform.
Zelensky told Ukrainian lawmakers: "We will not give up our rights to any part of our territory. Nor will we allow our state to be used in election battles in Europe. No one will win at Ukraine's expense."
Outlining his "resilience" plan, the Ukrainian leader urged citizens and officials to stand united, saying that the war had reached a critical juncture that would decide whether Ukraine or Russia prevails, according to Reuters.
Russia invaded Ukraine by land, air and sea on February 24, 2022, starting the largest military conflict in Europe since World War II.
Tuesday is day 1,000 of Russia's war on Ukraine.
Polish Prime Minister Donald Tusk has marked the sombre milestone in a social media post, honouring the heroism and suffering of the Ukrainian people and reaffirming Poland's solidarity with its embattled neighbour.