Ukrainian President Volodymyr Zelensky said in a news conference with the US president a "just peace" with Russia meant no compromises on Ukraine's sovereignty and territorial integrity.
President Joe Biden said the United States shared the same vision of a "free, independent, prosperous and secure Ukraine."
The presidents met at the White House and in what was Zelensky's first known overseas trip since Russia invaded Ukraine 300 days ago.
"Russia is using winter as a weapon," Biden said, referring to air strikes that have cut electricity. He said the Kremlin was "freezing people, starving people". He told the Ukrainian president "we will stay with you as long as it takes."
Ahead of Zelensky's arrival, the United States announced it provide another US$1.85 billion in military aid for Ukraine including a Patriot air defence system to help it ward off barrages of Russian missiles.
Zelensky called the missile defence system a "very important step to create secure airspace over Ukraine which would "significantly" strengthen the country's defence.
He also urged the US Congress to approve more funding, saying it would all "go towards strengthening our global security".
Ukraine's president Volodymyr Zelensky meets President Biden at the White House. Photo: AFP / Getty Images
Zelensky's political adviser Mykhailo Podolyak said earlier that the visit showed the deep trust between Kyiv and Washington and offered him the opportunity to explain what arms Kyiv needed.
"I will hold a series of negotiations to strengthen the resilience and defence capabilities of Ukraine," Zelensky said in a statement on Telegram alongside photos of him on US soil as he prepared to go into talks with Biden at the White House.
"Next year, we must return the Ukrainian flag and freedom to our entire land, to all our people," he said.
Wearing his trademark olive green pants and sweater, Zelensky arrived at the White House. He met Biden and his wife on the lawn and Biden guided the Ukrainian president with an arm around his back.
Following the news conference Zelensky was addressing a joint session of the US Senate and House of Representatives.
Ukraine in recent weeks has come under repeated Russian missile and drone strikes targeting its energy infrastructure, leaving millions of people without electricity or running water in the dead of a freezing winter.
The Patriot is deemed to be one of the most advanced US air defence systems, offering protection against attacking aircraft as well as cruise and ballistic missiles.
"...Weapons, weapons and more weapons. It is important to personally explain why we need certain types of weapons," Podolyak said. "In particular, armoured vehicles, the latest missile defence systems and long-range missiles."
Zelensky has made a point of staying close to his people during the war and advocating for his former Soviet state on the world stage, with daring trips to battlefronts, countless calls with world leaders and videolink speeches to parliaments and international institutions.
White House National Security Council spokesman John Kirby told MSNBC that diplomacy would be discussed with Zelensky, but the Ukrainian leader would be put under no pressure for peace talks.
Kirby said Washington was seeing no sign that Russian President Vladimir Putin was willing to engage in peacemaking.
"Clearly we're going to make sure that President Zelensky, when he leaves this country, knows that he's leaving with the full support of the United States going forward," Kirby told MSNBC in a separate interview earlier.
The Kremlin said on Wednesday it saw no chance of peace talks with Kyiv. In a call with reporters, spokesman Dmitry Peskov said that continued Western arms supplies to Ukraine would lead to a "deepening" of the conflict.
In a speech to defence chiefs in Moscow, President Vladimir Putin promised to give the military whatever it needed to prosecute a war nearing the end of its 10th month.
With the United States the largest military aid donor to Ukraine among Western allies, the Biden administration has provided about US$20 billion in assistance to Ukraine, including artillery ammunition, munitions for NASAMS air defence systems and for high mobility artillery rocket systems (HIMARS).
Zelensky has repeatedly called on the West to supply more advanced weaponry, ranging from modern battle tanks to missile defence systems.
US Senate Majority Leader Chuck Schumer, likened Zelensky's quest to Britain's WWII leader Winston Churchill, who sought US aid against Nazi Germany.
"Where Winston Churchill stood generations ago, so too President Zelensky stands not just as a president, but also as an ambassador of freedom itself," the top Senate Democrat said. "Now is not the time ... to take our foot off the gas when it comes to helping Ukraine."
- Reuters