Budapest finally made the move on Monday, with the parliament voting 188 to 6 in favor of the resolution.
Hungary’s Prime Minister Viktor Orbán, who has maintained contact with Russian President Vladimir Putin in defiance of Western pressure, withheld approval of Sweden's bid for more than 600 days.
Now, all existing NATO allies have ratified the membership status of Sweden. A flag-raising ceremony is expected at NATO headquarters in Brussels later this week, less than a year after fellow Nordic country Finland joined the alliance.
Orbán gave his final nod just before the weekend, when his Swedish counterpart Ulf Kristersson flew to Budapest and signed a defense deal following years of what Orbán called "damned" relations over human rights and the rule of law in his increasingly politically repressive country.
For now, Russia is the biggest loser of Sweden joining NATO.
Moscow has threatened Sweden and Finland since both countries turned toward NATO. Since the two Nordic countries began the process to join the alliance, the West has tightened its grip on the Baltic Sea, complicating a vital transit route for the Russian navy.