Felix Tshisekedi was declared winner of the long-delayed election amid suggestions of vote-rigging. Observers had seen another opposition candidate as leading the field to replace Joseph Kabila.
Election day delays kept polling stations open for hours after they were supposed to close in the capital Kinshasa, with one of the big issues attributed to new voting machines.
It has been over two years since President Joseph Kabila was scheduled to step down. But after Thursday's announcement, voters will have to wait a bit longer to finally cast their ballots.
Joseph Kabila is barred from seeking a third consecutive term as president of Congo, where elections are scheduled later this month. But he doesn't rule out running again in the future.