Official results are expected on Monday, but the independent monitors said the ranking of the candidates will not change and there will be no run-off because Vujanovic won more than 50 per cent of the votes cast.
Medojevic conceded defeat, with his party Movement for Change citing the same figures.
Turnout was 69 per cent, about 22 points higher than in 2003, when Vujanovic won his first five-year term, election observers said.
Vujanovic, of the ruling Democratic Party of Socialists - one of the staunchest advocates of Montenegro's split from Serbia - said his victory shows that "a majority of Montenegrins support our policies".
|Vujanovic: "I won for Montenegro |
and its future" [AFP]
"I won for Montenegro and its future," he told hundreds of his cheering supporters. "I will be the president of all the people in Montenegro."
Ethnic Serbs, who make up about 30 per cent of the population, are unhappy about Montenegro's separation from Serbia following a May 2006 referendum.
They are seeking closer political and economic ties with Belgrade, which have been chilly since the breakup.
Montenegro was an independent kingdom before World War I, then part of Yugoslavia until that nation disintegrated in violence in 1991. Montenegro remained joined with Serbia until it seceded peacefully.
Since the split, its economy has boomed. Annual economic growth is about 8 per cent and foreign direct investment since 2006 has been about $1.6bn, propelling Montenegro to the top of Europe's per capita foreign investment list.
But it has had trouble getting rid of its image as a society rife with corruption.
"The vote has shown that Montenegrins are still not ready for change of the corrupt and totalitarian regime," Medojevic, the liberal challenger, said.