The apex court affirmed the decision of the Court of Appeal which nullified the March 22 judgement of the Osun State election petition tribunal.
The tribunal had declared Ademola Adeleke of the Peoples Democratic Party as the winner of the September 2018 election.
The Supreme Court in a split judgement on Friday agreed substantially with the Court of Appeal which ruled that a majority judgement delivered at the tribunal was a nullity.
The court said the judge who had read the majority judgement at the tribunal, Peter Obiora, was evidently absent on February 6, following the documents before the court.
It said the failure of Mr Obiora to be present on that day meant that the tribunal lacked the authorities to have given any judgment on the matter.
Two of the seven members of the Supreme Court panel, however, disagreed with the ruling.
The Supreme Court ruling was read by Bode Rhodes-Vivour.