Opposition leader Felix Tshisekedi will be sworn in on Thursday as DR Congo's next president, sources said in Kinshasa, ending uncertainty about when the ceremony would take place.
The inauguration will take place at the Palace of the Nation, the seat of the presidency, starting at noon, aides to Tshisekedi and outgoing President Joseph Kabila said on Wednesday.
It will be the first peaceful transition of power in the history of the Democratic Republic of Congo, which gained independence from Belgium in 1960.
Tshisekedi, 55, will be taking the helm from Kabila who at only 47 has ruled the vast country for 18 years, succeeding his father Laurent-Desire, who was assassinated in 2001.
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.
Fayulu says he was winner, with 61 percent of the ballot, against 18 percent each for Tshisekedi and Emmanuel Ramazani Shadari, who was Kabila's preferred candidate.
He has angrily characterised the official result as an "electoral coup" cooked up by Kabila and Tshisekedi.
But he lost a challenge to the Constitutional Court, and foreign support for his position has waned, mainly to avoid the bloody confrontations that have marked the DRC's history.
The sprawling country suffered two regional wars in 1996-97 and 1998-2003, and the last two presidential elections, in 2006 and 2011, were marred by deadly clashes.
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.
Elections to the legislature were held on December 30 in parallel with presidential and provincial polls.
The Joint Front for Congo (FCC), which supports Kabila, controls 337 seats in the 500-member assembly against 102 for Fayulu's coalition, Lamuka, and 46 for the Heading for Change (Cach) coalition backing Tshisekedi, according to a provisional UN tally.
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.