The 12 June 1993 presidential election — the cleanest in Nigerian history, monitored by the Centre for Democratic Studies and the National Electoral Commission under Professor Humphrey Nwosu — was contested between Chief Moshood Kashimawo Olawale (MKO) Abiola of the Social Democratic Party (SDP) and Alhaji Bashir Tofa of the National Republican Convention (NRC). Provisional results compiled by the press from polling-station declarations gave Abiola 8.34m votes (58.4%) to Tofa's 5.95m, with Abiola winning his opponent's home state of Kano.
On 16 June 1993 the Abuja Federal High Court (Justice Bassey Ikpeme) granted an ex parte injunction obtained by the Association for Better Nigeria (a body fronted by Abacha-aligned politician Arthur Nzeribe) restraining the NEC from announcing the results. On 23 June 1993 General Ibrahim Babangida issued the Constitution (Suspension and Modification) (Amendment) Decree No. 13 of 1993 — formally annulling the election. No reason consistent with the published evidence was ever offered.
The protests of June–August 1993 — coordinated by the Campaign for Democracy under Dr Beko Ransome-Kuti, the NADECO front, the NLC under Pascal Bafyau, and the National Association of Nigerian Students — paralysed Lagos, Ibadan, Abeokuta and the south-west. Approximately 100 demonstrators were killed by security forces between July and August 1993. Babangida 'stepped aside' on 26 August 1993, installing the Interim National Government of Chief Ernest Shonekan; Shonekan was deposed by Sani Abacha on 17 November 1993.
Abiola declared himself President at Epetedo, Lagos on 11 June 1994 and was arrested for treason on 23 June 1994. He died in custody at Aguda House, Abuja, on 7 July 1998 — the day of his scheduled release — under contested circumstances during a meeting with US Assistant Secretary of State Thomas Pickering. His widow Kudirat Abiola had been assassinated by Abacha's hit squad on 4 June 1996. June 12 was finally recognised as Democracy Day by President Muhammadu Buhari in 2018; Abiola was posthumously awarded the GCFR. The annulment remains the archetypal stolen mandate of Nigerian politics, the unwritten reference of every subsequent electoral crisis (2007, 2011, 2019, 2023).