It held that the All Progressives Congress and its candidate, Gboyega Oyetola, were not validly returned.
The Justice Ibrahim Sirajo-led three-man bench began delivering judgment at 10.33am on Friday.
The lead judgment was delivered by a member of the panel, Justice Peter Obiora.
It can be recalled that the Independent National Electoral Commission declared the candidate of the All Progressives Congress, Gboyega Oyetola, as the Governor-elect of Osun State, on the 28 of September, 2018.
The rerun of the Osun State governorship election was held in seven polling units across four council areas with the candidate of the All Progressives Congress, Gboyega Oyetola, beating the Peoples Democratic Party candidate, Ademola Adeleke.
The returning officer, Prof. Joseph Fuwape, declared that the APC candidate, Oyetola, won the governorship election by scoring a total number of 255,505 votes while Adeleke of the PDP polled 255,023 votes.
This was, however, met with protests by Adeleke, the PDP, and the Coalition of United Political Parties, among others.