NATO Secretary General Jens Stoltenberg says Finland will join NATO on Tuesday, citing the completion of approval procedures by all member states.
Stoltenberg said, "This is a historic week. Tomorrow, we will welcome Finland as the 31st member of NATO - making Finland safer and our alliance stronger."
He also said a flag raising ceremony will take place at NATO headquarters on Tuesday afternoon.
All 30 NATO nations have to approve any new members.
Turkish lawmakers added their approval last week, after months of talks with the country. Turkey raised objections, arguing that Finland was soft on terrorism.
Turkish leaders are keeping Sweden's application on hold, saying the country has not done enough to crack down on Kurdish groups they consider to be terrorists.
Meanwhile, Russia has reacted sharply to NATO's addition of a new member.
State-owned news agency RIA says officials have announced plans to strengthen Russia's military capacity in its western and northwestern regions.