The Centre for Free Elections and Democracy said the projected result was 55.3% in favour of independence, lower than an earlier projection of 56.3%, and just surpassing the 55% threshold required for the outcome to be validated.
Waves of celebratory gunfire and fireworks thundered across the capital Podgorica moments after the unofficial result was broadcast and crowds of mostly young people rushed towards the main boulevards of the capital waving the red-and-gold flag of Montenegro and sounding their horns.
But the anti-independence camp refused to concede defeat, saying the celebrations were premature.
Turnout for the ballot was 88%, poll analysts said, a fact which would lend legitimacy to the process and to the creation of Europe's newest state and one of the smallest in terms of population.
If upheld by official results due early on Monday, the outcome will dissolve a partnership with Serbia going back to 1918 in various forms.
Montenegro would be the last of former Yugoslavia's six federal republics to part company with Serbia since 1991.
The mountainous Adriatic republic has only 650,000 people but pro-independence leaders say it has a better chance of economic prosperity on its own than in a dysfunctional union with Serbia.