"The court has unanimously determined that the petitions are not merited. As a consequence, the presidential election of 26 October is hereby upheld as is the election of the third respondent," said Chief Justice David Maraga, referring to Kenyatta.
The ruling paves the way for Kenyatta to be sworn in on November 28, bringing to a close what has been a divisive and bloody election process.
Maraga had in September annulled an August 8 election due to "irregularities and illegalities", in a historic decision hailed across the globe as an opportunity to deepen Kenyan democracy.
But the ruling only deepened acrimony, sparking further protests as opposition leader Raila Odingadecided to boycott the October vote -- handing Kenyatta a 98 percent victory.