Denis Sassou Nguesso has been tipped favourite by many within the party who will consider failure to choose him as a big surprise.
Sassou-Nguesso, 71, led the country from 1979 to 1992 and then returned to power at the end of a civil war in 1997. He was elected in 2002 and 2009 in elections whose results were disputed by the opposition.
He has the chance to stand this year’s election after amending the country’s constitution through a referendum in October 2015.
The opposition called for a boycott of the poll and one of its leaders described the official results as a “fraud.”
In late September, thousands of people demonstrated in a rare protest in Brazzaville.
Slogans such as “Sassou out!” echoed through Brazzaville’s central Boulevard as some protesters carried banners reading “Sassoufit,” a word game that means “that’s enough” in French, the nation’s official language.
Despite criticisms, the referendum received crucial support from former colonial master France, whose President, Francois Hollande, spoke of “President Sassou-Nguesso’s right to consult the people.” President Macky Sall of Senegal also supported the referendum.