In a speech posted on his X social media account, Matata Ponyo said he would throw his support behind Moise Katumbi, a millionaire businessman and former governor of the copper-rich Katanga region.
Katumbi is expected to launch his campaign for the Dec. 20 election on Monday.
Representatives of Congo's main opposition parties held talks this week in Pretoria on how to ensure the general election would be fair and to decide on a potential joint candidate to challenge President Felix Tshisekedi.
Opposition parties are concerned that the election will be flawed, and have alleged irregularities during the voter registration period which they said were orchestrated by the national election commission to favour Tshisekedi's ruling coalition.
The commission has denied the accusation, promising a fair election.
"In a bid to do whatever it takes to remain in power, this regime has intelligently put in place a complex system of electoral fraud and corruption," Matata Ponyo said in a speech on Sunday night.
He said the best strategy for the opposition was to back a joint candidate.
"Following consultations held in Pretoria, Moise Katumbi emerges as the candidate that could lead the opposition ticket represented by four major parties and groups that took part in this discussion," he said, without naming the parties.
"In line with the decision of my party, I want to announce that I'm dropping my bid in the presidential race of Dec. 20 in favour of Moise Katumbi," he said, calling on other parties to back Katumbi.
Martin Fayulu, one of Congo's main opposition leaders who launched his campaign on Sunday, had also sent representatives to the Pretoria meeting.
"I did not choose to go it alone, it was the others who excluded my delegates during the talks in Pretoria," Fayulu, who launched his campaign in Bandundu, in the west of the country, told Reuters by telephone on Sunday night.
(Reporting by Ange Kasongo in Kinshasa and Sonia Rolley in Paris; Writing by Bate Felix; Editing by Alex Richardson)
