The US Senate on Wednesday voted to approve Finland and Sweden's accession to Nato, the most significant expansion of the 30-member alliance since the 1990s as it responds to Russia's invasion of Ukraine.
The Senate voted 95 to 1 to support ratification of the two countries' accession documents, easily passing the two-thirds majority of 67 required to support ratification of the two countries' accession documents.
"This historic vote sends an important signal of the sustained, bipartisan US commitment to Nato, and to ensuring our Alliance is prepared to meet the challenges of today and tomorrow," US President Joe Biden said.
Sweden and Finland applied for Nato membership in response to the invasion of Ukraine by Russia, which has repeatedly warned both against joining the alliance.
"I look forward to signing the accession protocols and welcoming Sweden and Finland, two strong democracies with highly capable militaries, into the greatest defensive alliance in history," Mr Biden said.
Nato's 30 allies signed the accession protocol for them last month, allowing them to join the US-led nuclear-armed alliance when its members ratify the decision.
"It will advance the cause of democracy," Senate majority leader Chuck Schumer tweeted after the vote.
"And it is all the more urgent given [Russian President Vladimir] Putin's barbaric, immoral and unjustified war in Ukraine."
Helsinki and Stockholm have been able to take part in Nato meetings and have greater access to intelligence.
But they are not yet protected by Article 5, the Nato defence clause stating that an attack against one ally is an attack on all.
The accession must be ratified by the parliaments of all 30 North Atlantic Treaty Organisation members before Finland and Sweden can be protected by the defence clause.
Ratification could take up to a year, although it has already been approved by a few countries including Canada, Germany and Italy.
Mr Biden called Wednesday's vote the culmination of "the fastest Senate process for a Nato protocol since 1981".
Senators from both parties strongly endorsed membership for the two countries, describing them as important allies whose modern militaries already worked closely with Nato.
"The qualifications of these two prosperous, democratic nations are outstanding and will serve to strengthen the Nato alliance," said Democratic Senator Bob Menendez, chairman of the foreign relations committee, urging support before the vote.
Senate majority leader Chuck Schumer invited the ambassadors and other diplomats from Finland and Sweden to the Senate to observe the vote.
Republican Senator Josh Hawley was the lone "no" vote. Republican Senator Rand Paul voted present.
Reuters contributed to this report