The government also honoured Abiola with the Grand Commander of the Federal Republic (GCFR) title.
The President announced this in a statement issued via his Twitter handle on Wednesday, June 6, 2018.
He also awarded Abiola the highest honour in the nation - Grand Commander of the Federal Republic (GCFR).
With Buhari's declaration, June 12 will now replace May 29 as Democracy Day. He said June 12 is a more symbolic day.
He said, "Dear Nigerians, I am delighted to announce that, after due consultations, the Federal Government has decided that henceforth, June 12 will be celebrated as Democracy Day.
"We have also decided to award posthumously the highest Honour in the land, GCFR, to the late Chief MKO Abiola.
"In the view of Nigerians, as shared by this Administration, June 12, 1993, was and is far more symbolic of Democracy in the Nigerian context than May 29, or even October 1".
The President also conferred a national honour on Baba Gana Kingibe and recognised the role of late Gani Fawehinmi in the actualisation of June 12 elections.
"Chief Abiola’s running mate, Ambassador Baba Gana Kingibe, is also to be awarded a GCON.
"Furthermore, the late Chief Gani Fawehinmi, SAN, a tireless fighter for human rights and democracy, and for the actualisation of the June 12, 1993 elections, will be posthumously awarded a GCON," he added.
Buhari also acknowledged that the June 12, 1993 election was the freest, fairest and most peaceful election Nigeria ever conducted since Independence.
"June 12, 1993, was the day millions of Nigerians expressed their Democratic will in the freest, fairest and most peaceful elections since our Independence. That the outcome of that election was not upheld by the then military Govt does not detract from its democratic credentials," he said.
He said a commemorative and investiture event has been fixed for Tuesday, June 12, 2018.