The formal submissions came after a dizzying week that began when Mr. Niinisto and Finland’s prime minister, Sanna Marin, announced their support for membership last Thursday. Finland’s Parliament endorsed the proposal on Tuesday in a vote of 188 to 8. The vote was a political formality, because Mr. Niinisto has authority over the nation’s foreign policy, but it served as a signal of enthusiasm in a country where public opinion in favor of joining NATO has moved from 20 percent before the Russian invasion to nearly 80 percent now.
“This was an exceptionally strong result, 188 votes in favor,” Finland’s foreign minister, Pekka Haavisto, told the Finnish broadcaster YLE. “I did not myself expect such a strong outcome.” Mr. Haavisto signed the country’s application after the vote.
The Finnish government has closely coordinated its moves with Sweden, a longstanding security partner that has observed neutrality for two centuries but whose public has also moved staunchly in favor of joining NATO.
On Sunday, Sweden’s governing Social Democratic Party cast aside decades of misgivings and announced its decision to support the bid for accession to NATO. Fifty-seven percent of the Swedish public now supports joining the alliance, up from 48 percent at the end of April, according to a poll by the Dagens Nyheter newspaper. Sweden’s foreign minister, Ann Linde, signed her country’s NATO application on Tuesday morning.
Sweden’s prime minister, Magdalena Andersson, said that her nation was closely bound with Finland. “This is a strong and clear signal that we stand united,” she said.
The triumphant mood in the Nordic states was shadowed, however, by signals that Turkey, a NATO member, might seek to block their accession. The Turkish president, Recep Tayyip Erdogan, has sharply criticized Sweden in particular as a haven for Kurdish separatists he regards as terrorists.
Mr. Niinisto has said that he was surprised by Mr. Erdogan’s comments, and expressed hope that any differences could be worked out in direct talks with Turkey.