Sweden has decided to follow Finland and apply for NATO membership in the wake of Russia's invasion of Ukraine, ending more than 200 years of military non-alignment.
Prime Minister Magdalena Andersson called it "a historic change in our country's security policy" as she addressed legislators in the Swedish capital Stockholm.
"Sweden needs formal security guarantees that come with membership in NATO," Ms Andersson said, adding that the country was acting together with Finland, whose government announced on Sunday it would seek to join the alliance.
The announcement came after a debate in parliament showed that there is a huge support for joining NATO.
Ms Andersson's Social Democratic Party broke with the party's long-standing position that Sweden must remain non-aligned, paving the way for a clear majority for NATO membership in the parliament.
"The Swedish government's intent is to apply for NATO membership. A historic day for Sweden," Foreign Minister Ann Linde wrote on Twitter.
"With a broad support from political parties in the parliament, the conclusion is that Sweden will stand stronger together with allies in NATO."
Once a regional military power, Sweden has avoided military alliances since the end of the Napoleonic Wars.
Like Finland, it remained neutral throughout the Cold War but formed closer relations with NATO after the Soviet collapse in 1991.
Watch: 'Moment of significant changes' as ministers from Finland and Sweden join NATO meeting in Berlin.
Public opinion in both countries was firmly against joining NATO until Russia's invasion of Ukraine, after which polls indicated a dramatic shift in favour of membership.
The governments in Finland and Sweden responded by swiftly initiating discussions across political parties about NATO membership and reaching out to the US, UK, Germany and other NATO countries for their support.
The Kremlin has repeatedly warned the move would have destabilising consequences for security in Europe.
Russian President Vladimir Putin said on Monday that Moscow "does not have a problem" with Sweden or Finland as they apply for NATO membership, but that "the expansion of military infrastructure on to this territory will of course give rise to our reaction in response".
Prime Minister Boris Johnson recently signed historic security assurance declarations with Sweden and Finland, pledging to "bolster military ties" and support both countries should they come under attack.
Watch: Why Finland wants to join NATO.
Although NATO officials have expressed hopes for a quick ratification process, all 30 current NATO members must agree to let Finland and Sweden in the door.
Turkey voiced some objections, accusing the two countries of supporting Kurdish militants and others whom Turkey considers to be terrorists.
Swedish defence minister Peter Hultqvist told public broadcaster SVT that a Swedish delegation would be sent to Ankara to discuss the issue.