During bilateral meetings at the White House, which included Vice President Kamala Harris and Secretary of State Antony Blinken, Mr Biden announced a new military aid package that includes artillery, ammunition, anti-tank weapons and Abrams tanks, which will be delivered to Ukraine next week.
“We are also focused on strengthening Ukraine's air defence capabilities to protect the critical infrastructure that provides heat and light during the coldest and darkest days of the year,” Mr Biden said.
“That includes providing the second Hawk air defence battery, with steady deliveries of additional Hawk and other systems each month through the winner.”
Mr Zelenskyy thanked Mr Biden for the new tranche of aid and said the two leaders had held “very productive, strong negotiations”.
“I thank the United States of America, Mr President for the new defence package for Ukraine, a very powerful package,” he said. “Thanks so much, and it has exactly what our soldiers need.”
Earlier, Mr Zelenskyy said “air defence” was one of his top priorities amid missile strikes on Ukrainian cities.
“More air defence, more support for Ukrainian soldiers on the front lines,” he said.
Earlier on Thursday, Mr Biden and his wife Jill greeted Mr Zelenskyy and his wife Olena outside the White House before the two leaders held a meeting in the Oval Office.
And in the morning, Mr Zelenskyy held private meetings with Republican and Democratic politicians in Congress as he pushed for sustained US support for his country's war effort.
He also spoke with top military leaders at the Pentagon, including Defence Secretary Lloyd Austin.
US National Security Adviser Jake Sullivan said the new package of military assistance includes more ammunition for US-provided Himars systems, anti-armour missiles, artillery shells and DPICMs, which are surface-to-surface missiles.
Mr Zelenskyy was hoping the US would approve sending F-16 fighter jets as well as Army Tactical Missile Systems, or ATACMS – long-range missiles that Kyiv has long sought to obtain – to the country.
“It was great to meet with President Zelenskyy today,” House foreign affairs chairman Michael McCaul said on X, formerly Twitter.
“It is critical Ukraine win this war as the enemies of freedom … are watching closely. I pledged to continue pushing President Biden to send ATACMS.”
The trip marks Mr Zelenskyy's second visit to the White House since Russia's invasion.
The meeting in Washington comes at a critical time, Mr Kirby said, as Russian President Vladimir Putin has reached out to North Korea for ammunition and weapons, and is getting drones from Iran.
“We're going to continue to do what we can to help them achieve success in this counter-offensive – and beyond, quite frankly,” John Kirby, the White House National Security spokesman ton Wednesday.
Ukraine launched its counter-offensive against Russian forces in early June to try to reclaim territory taken during the full-scale invasion that started in February 2022.
But progress has been slow, making it increasingly difficult for Mr Biden, who is running for re-election in 2024, to advocate for more funding for Ukraine.
Mr Kirby said Ukraine was making some progress but that “clearly, this counter-offensive is not over”, and would require more support to continue making advances.
Meanwhile, Congress is debating whether or not to approve $24 billion in additional assistance to Ukraine, which Mr Biden has requested.
But amid intense partisanship between Democrats and Republicans, Congress is increasingly divided over providing more funds for a war that is showing no sign of abating.
House Speaker Kevin McCarthy turned down a request by Mr Zelenskyy to address a joint session of Congress, media outlets reported.
Since the war began, Mr Biden has directed about $75 billion in military, financial and humanitarian assistance to Ukraine.
“If you think that the cost of supporting Ukraine is high now, just ponder how exorbitantly higher it would be in blood and treasure if we just walk away and let him [Mr Putin] take Ukraine,” Mr Kirby said.
“Then the cost of defending sovereign integrity and territory, believe me, gets a whole lot more expensive in both blood and treasure, including American blood.”
Republicans have a narrow majority in the US House of Representatives and have indicated that they are opposed to more funds for Ukraine.
Some conservative politicians are pushing for broad spending cuts and an end to all military aid to Ukraine.