Lawyers for the MDC argued that the results should be annulled due to “massive doctoring” of the July 30 vote.
Mnangagwa, of the ruling ZANU-PF party, won the election with 50.8 percent of the vote — just enough to meet the 50 percent threshold needed to avoid a run-off against MDC leader Nelson Chamisa, who scored 44.3 percent.
Nine judges, led by Chief Justice Luke Malaba, are hearing the case in Harare, amid tight security.
But in a first for the country, the proceedings have been broadcast live on state television.
The court could declare a winner, call another election, or order a run-off or recount.
The inauguration should take place within 48 hours of the court’s ruling, according to the constitution.