André Okombi Salissa, who served as a minister under Sassou Nguesso, has joined the presidential race.
He made the announcement on Saturday in front of party supporters who turned out for the event.
Okombi Salissa became an opposition leader in 2012.
“My fellow countrymen, you will have to choose between inertia and dynamism, the past and the future, praise singing and humility at the service of the people,” Salissa said.
The opposition has been blamed for its inability to form a coalition against Denis Sassou Nguesso who will seek another mandate in the March 20 election.
André Okombi Salissa, 54, was born in Plateaux and served as minister of higher education, sports, transport and social security.
The Congo Democracy Initiative coalition which he will lead during the March 20 polls is one of the two major coalitions in Congo which contested the October 2015 referendum. It is made up mainly of former close collaborators of President Sassou.
Another, the Republican Front for the Respect of the Constitution and Democratic Change is also made up of major opposition leaders.
Denis Sassou Nguesso has been chosen as the presidential candidate for the Congolese Labour Party for the upcoming presidential election.