Felix Tshisekedi will be sworn in as president of the Democratic Republic of Congo in a ceremony in the capital, Kinshasa, later on Thursday.
Tshisekedi was declared winner of the thrice-delayed election with 38.5 percent of the vote, while Martin Fayulu, who also comes from the opposition, was credited with 34.8 percent
It will be the first peaceful transfer of power in the country, but there remain questions about the legitimacy of Mr Tshisekedi’s victory.
A BBC correspondent in Kinshasa said there is no desire among the population to begin a campaign of protests against the result, rather that they are pleased that the country has taken a step towards entrenching democratic norms.
But it is likely that outgoing President Joseph Kabila will continue to play a leading role in the country.
His party is the biggest in the new parliament and there is a widespread belief that he engineered Mr Tshisekedi’s victory to ensure he will still be able to dictate policy.
Tshisekedi is the son of the late veteran opposition leader Etienne Tshisekedi, who died in February 2017, aged 84.
One of his first tasks in office will be to choose a prime minister, set to come from pro-Kabila lawmakers who dominate the National Assembly.
The presidential inauguration had initially been scheduled for Tuesday, but was postponed in order to give more time for preparations, notably invitations to foreign VIPs.