Ukraine's President Volodymyr Zelenskyy thanked Biden for his "unwavering support," while German Chancellor Olaf Scholz said the "decision not to run again deserves recognition".
ADVERTISEMENTTributes have been paid from across Europe to Joe Biden who announced on Sunday he was pulling out of the presidential race and endorsing his Vice President Kamala Harris to replace him at the top of the ticket.
In a written statement, Biden said it had been the greatest honour of his life to serve as president and vowed to stay in the job until his term ends in January.
"I will speak to the nation later this week in more detail about my decision," he said.
From Ukraine, President Volodymyr Zelenskyy thanked Biden for his "unwavering support" in the two years since the Russian invasion.
"We will always be thankful for President Biden’s leadership," he said, adding, "We respect today's tough but strong decision."
The US, under Biden, has been Ukraine's main financial and military backer, and there are concerns in both countries that support could stop if Donald Trump wins November's presidential election.
Germany's Chancellor Olaf Scholz referred to Biden as "my friend," adding, "Thanks to him, transatlantic cooperation is close, NATO is strong, and the US is a good and reliable partner for us. His decision not to run again deserves recognition."
Poland's Prime Minister Donald Tusk praised Biden for his "difficult decisions", which he said made "Poland, America and the world safer".
He also said the decision to drop out of the presidential race was probably "the most difficult" decision Biden had had to make.
"All my admiration and recognition for the brave and dignified decision of the president," began Spain's PM Pedro Sánchez.
"A great gesture from a great president who has always fought for democracy and freedom," he said.
UK Prime Minister Keir Starmer said, "I respect President Biden’s decision and I look forward to us working together during the remainder of his presidency."
Starmer added that he knew that Biden had "made his decision based on what he believes is best for the American people."
Closer to home, VP Harris thanked Biden for his "extraordinary leadership" and said she was honoured to have his endorsement to run for the White House.
Former President Barack Obama, under whom Biden served as Vice President, described him as "one of America’s most consequential presidents" and said he was a "patriot of the highest order."
ADVERTISEMENTFormer House Speaker and Democratic colleague Nancy Pelosi sent "love and gratitude" to Biden, adding, "God blessed America with Joe Biden’s greatness and goodness."