Seven opposition Gambian parties closed ranks and chose a sole candidate to contest against long-serving incumbent Yahya Jammeh in presidential polls in December.
The candidate, Adama Barrow, was elected through primaries in a convention attended by 490 delegates.
The 51-year-old from the United Democratic Party, the country's biggest opposition movement, got 308 of the 487 votes cast.
"We have put our differences aside for the interest of this country. Gambians are tired of 22 years of Yahya Jammeh?s misrule and will end it come December 1st when we go to the polls. We all have to put our hands together to save this country from destruction," he said.
This is the biggest opposition alliance in the history of The Gambia, a former British colony.
Jammeh, 51, came to power in a 1994 coup, and has ruled The Gambia with an iron fist since.
His regime is also regularly accused by rights groups of arranging the forcible disappearance of opponents.
Before the nation's last presidential vote in 2011, the 15-nation Economic Community of West African States (ECOWAS) said Jammeh's control of the media and intimidation of voters meant the election could not be free and fair.
The strongman took 73 percent of the vote.
The Gambia's newly appointed Independent Electoral Commission has assured political parties the upcoming vote will not be rigged, despite fears that an opposition crackdown is already underway.