The conferment of the honour on the late Moshood Kashimawo Olawale Abiola comes 25 years after the election, which is recognised as the freest in the country’s history.
It comes almost 20 years after Abiola died in detention after being jailed by military dictator General Sani Abacha for trying to claim his mandate.
President Buhari also apologised to the family of the late Chief Moshood Abiola for the annulment of the June 12, 1993 presidential election which he won.
Buhari said his decision to revisit the annulled election was not an attempt to open an old wound but to put right what has wrongly been done.
He said it was clear that Abiola was already winning the election when the government of the day inexplicably cancelled it.
He said Nigerians will no longer tolerate such traversal of justice.