With nearly all ballots from Sunday's referendum counted, 55.4 percent of voters chose independence for the republic.
That is just over the 55 percent threshold needed for the referendum to be valid under rules set by the European Union.
Prime Minister Milo Djukanovic, speaking before the commission announcement, said: "I'm sure that tonight a democratic Montenegro will be celebrated."
Djukanovic's Democratic Party of Socialists had pushed for Montenegro's full independence.
Opposition spokesman Predrag Bulatovic disputed early projections, saying supporters fell short of the required margin of victory. But Predrag Sekulic, a spokesman for Djukanovic's party, said, "There is no doubt we won."
People began celebrating inside government buildings Sunday night, and fireworks illuminated the center of the Montenegrin capital Podgorica.
At stake is whether Europe will see the formation of a new country. Montenegro would be a small, mountainous nation along the Adriatic Sea with a total population of about 650,000 residents.
Montenegro had been one of six republics within Yugoslavia before the country's violent unraveling in 1991. In 2003, after nearly a decade of war and political upheaval, Serbia and Montenegro replaced what remained of the Yugoslav federation with a loose union.
Djukanovic has pushed for full independence, arguing the country would have a better chance of joining the European Union if separated from Serbia.
That argument was bolstered in the last month, when Serbia's Belgrade government failed to deliver Gen. Ratko Mladic, an indicted Serb war criminal, to a U.N. war crimes tribunal in The Hague.
Once an independent kingdom, Montenegro was erased from the map after World War I and merged into the newly formed Yugoslavia. Many Montenegrins resisted, and a seven-year guerrilla war followed. After World War II, the six-republic Yugoslavia became communist.
During the federation's breakup in the 1990s, Montenegro's leaders sided with Serbian President Slobodan Milosevic -- who would later stand trial for war crimes -- in his war campaigns in Slovenia, Croatia and Bosnia.
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