Tchiroma Bakary previously told the BBC that he would not accept a stolen vote.
He said his team had compiled the overall picture based on results from individual polling stations.
In a video statement posted on social media, Tchiroma Bakary said he had won the election with about 55% of the vote, based on what he said were returns representing 80% of the electorate.
The 76-year-old former government minister broke ranks with Biya, 92, who is seeking another term after 43 years in power.
CPDM has dismissed Tchiroma Bakary’s victory claims and several officials have described it as illegal because only the constitutional council can proclaim official results.
Opposition supporters have alleged that the 12 October poll was marred by irregularities, including ballot-stuffing.
Judges on the constitutional council dismissed eight petitions, citing insufficient evidence of irregularities or a lack of jurisdiction to annul results.
Tchiroma Bakary refused to file complaints with the council, whose judges have been appointed by Biya, choosing instead to declare himself the “legal and legitimate president”.
Born in Garoua, Tchiroma Bakary trained as an engineer in France before returning to Cameroon to work for the national railway company.
In 1984, he was thrown in jail, accused of being involved in an attempt to depose President Biya. Despite denying the allegation and never being convicted, Tchiroma Bakary spent six years in prison.
He also served as communications minister from 2009 to 2019.
In this role and as the government’s spokesperson, he resolutely defended Biya’s government during crises such as the Boko Haram insurgency, when the army was accused of killing civilians.
But in June, just four months before the general election, Tchiroma Bakary changed course dramatically, resigning from the government and announcing he would run against Biya for the presidency.
