Felix Tshisekedi will run for president in December's elections in Democratic Republic of Congo with Vital Kamerhe as his running mate, the two opposition leaders said on Friday in Nairobi.
"We are here to sign an agreement for a ticket to go together to elections," Kamerhe said at a joint press conference in the Kenyan capital.
"I decide today to support Tshisekedi as the president of Congo."
The two prominent leaders had previously agreed to back a unity opposition candidate, Martin Fayulu, against Emmanuel Ramazani Shadari, President Joseph Kabila's hand-picked successor in the December 23 poll.
But they pulled out of the alliance leaving the opposition weakened and in disarray.
Their decision to run on a single ticket shakes up the election exactly a month before the vote.
Tshisekedi is the son of Congo's most famous oppositionist, Etienne Tshisikedi, while Kamerhe ran in 2011.