Republicans in Congress have been blocking tens of billions of dollars in military assistance for Kyiv for months.
"It is necessary to specifically tell Congress that if Congress does not help Ukraine, Ukraine will lose the war," Zelensky said during a video meeting of Kyiv-organised fundraising platform United24.
Zelensky said it would be "difficult" for Ukraine to "stay" (survive) without the aid.
He said that "if Ukraine loses the war, other states will be attacked."
Russia's invasion of Ukraine has dragged on for more than two years.