"The Zimbabwe presidential election held on 31st July, 2013 was in accordance with the laws of Zimbabwe," said Chief Justice Godfrey Chidyausiku on Tuesday.
"The said election was free, fair and credible."
Mugabe was declared the winner in general elections on July 31 with 61% of the ballot, against his main rival Morgan Tsvangirai's 34%.
Local observers have called the polls flawed and Western powers have raised serious doubts over the vote, but regional organisations the African Union and Southern African Development Community were less critical.
Tsvangirai condemned the election as "a farce" and "a massive fraud" and demanded a forensic audit of the election results, voters' registers and numbers of voters who were turned away and those who were issued with certificates to vote.
He filed a petition two weeks ago challenging Mugabe's re-election vowing expose how the vote was rigged to hand Mugabe victory.
In a surprise U-turn Friday, Tsvangirai withdrew his petition saying he would not get a fair hearing.
He said the courts had frustrated his efforts for the release of election materials to use as evidence.
But the Constitutional Court went ahead and made a ruling on the case, clearing the way for Mugabe's inauguration on Thursday. – AFP