"I announce that the parliament of Montenegro voted for the proclamation of independence of Montenegro," Ranko Krivokapic, the speaker of the parliament, said after the assembly's unanimous vote on Saturday.
"The Republic of Montenegro is an independent state with full international and legal legitimacy within its existing borders," the statement of proclamation read out by Krivokapic, said.
The proclamation came after an EU-appointed Slovak diplomat Frantisek Lipka, the chairman of the referendum commission, reported that the majority of Montenegrin voters had supported separation from Serbia in the May 21 referendum.
According to official results 55.5% of some 420,000 voters on May 21 supported independence, narrowly passing the 55% threshold set by the EU.
The mountainous republic of 650,000 people is the last of ex-Yugoslavia's constituent republics to formally secede from Belgrade.
Montenegro is Serbia's closest ally and the split ends a long, fraternal partnership whose dissolution was opposed by ethnic Serbs who live in Montenegro.
"The Republic of Montenegro is an independent state with full international and legal legitimacy within its existing borders"
Montenegrin proclamation of independence
Serbia and Montenegro were the last two republics to remain allied after the bloody break-up of federal Yugoslavia in the early 1990s.
Vojislav Kostunica, the Serbian prime minister, responded frostily to the Montenegrin decision and on Friday rebuffed European Union offers to assist the two countries in a "velvet divorce", indicating the parting will be correct but not amicable.
Saturday's declaration was a relatively low-profile event.
When the preliminary referendum results were released two weeks ago people celebrated in the streets of Podgorica with noisy car cavalcades, fireworks and Balkan-style celebratory gunfire.
Montenegro plans to have its an independence day celbration on July 13, which is currently its "statehood day".