The NDC leader, who contested the presidential primaries unopposed for the second time, received 1, 199,118 YES votes in elections held across 265 constituencies over the weekend.
The figure represents 95.1 per cent of total votes cast, according to the Electoral Commission of Ghana.
There were 61, 836 NO votes, representing 4.9 per cent of valid votes cast.
Over 25,000 votes were rejected.
Speaking after his declaration as flagbearer of the NDC, President Mahama expressed satisfaction with the conduct of the primaries despite challenges at some centers.
“This new system might not be perfect but it is certainly better than the system we used previously.”
He touted the expansion of the electoral college into general suffrage as the first by any political party in the world.
He considered the NO votes received as either an error on the part of members or deliberately done.