Mahama has been president since President Mills died this summer. (World Food Programme)

Mahama won over challenger Nana Akufo-Addo with 50.7 percent of the vote. An estimated 11 million Ghanains voted, a roughly 80% turnout of the voting population. But new biometric machines used to identify voters failed in large numbers and voting days had to be extended.

The New Patriotic Party has accused the National Democratic Party of rigging the election to win Mahama's victory, according to the BBC.

"This situation, if allowed to go unchallenged and uncorrected, would seriously damage the essence of the electoral process and the substance of democracy in Ghana," the NPP said.

Ghana has held non-violent elections and peaceful transitions of power since 1992, an impressive record for an otherwise troubled corner of West Africa. Despite more than a decade of peace, many worry what the impact of a disputed election will look like. 

From USA Today:

Ghana's history and its record of democratic progress is not that different from that of nearby Mali, a nation also considered a model democracy until a coup this spring.

The outcome of the election will hinge on whether the 68-year-old Akufo-Addo will accept the results. Neighboring Ivory Coast was dragged to the brink of civil war last year, after that race's loser refused to accept defeat.

Mahama has been president since the death of President John Atta Mills in July. He defeated six cadidates along with Akufo-Addo and was elected to a four-year term, according to Bloomberg.

“I call on all leaders of political parties that participated in this election to respect the voice of the people,” Mahama told reporters. “We must celebrate together as Ghanaians and let’s refrain from any act that will disturb the peace and order that this country continues to enjoy.”

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[View the story "Ghana's election is over but the controversy rages on:" on Storify]