Wealthy businessman and former governor of the southeast Katanga Province was once an ally of former President Joseph Kabila but after a falling-out, Katumbi was charged with property fraud and barred from running in December's election.
That vote was won by Felix Tshisekedi, who has pardoned 700 prisoners including the political opponents of former President Kabila.
Moise Katumbi was among those cleared and now he wants to unite the opposition.
Al Jazeera's Catherine Soi reports from Lubumbashi.
