Biden told the crowd of several thousand people gathered outside the Royal Castle i n Warsaw that "Kyiv stands strong, Kyiv stands proud, it stands tall and most importantly it stands free."
"A dictator bent on rebuilding an empire will never be able to ease the people's love of liberty, brutality will never grind down the will of the free," he added.
Biden also responded to an anti-West speech made by Russian President Vladimir Putin earlier Tuesday, in which the Russian leader claimed the Ukraine war as a means of destroying Russia.
The Russian leader accused Western powers of wanting "to be done with us once and for all", but said increasingly stringent sanctions on Russia "will not succeed."
"The West is not plotting to attack Russia as Putin said today," Biden said.
"Millions of Russian citizens who only want to live in peace with their neighbors are not the enemy."
Biden stressed the West's continued support for Ukraine.
Putin "thought autocrats like himself were tough and leaders of democracy were soft and then he met the iron will of America and nations everywhere that refused to accept a world governed by fear," he said.
"There should be no doubt: our support for Ukraine will not waver, NATO will not be divided and we will not tire."
The official visit to Poland is Biden's second in the past 12 months.
On Wednesday, he will meet in Warsaw with the leaders of nine countries on NATO's eastern flank.