Before his appointment as the Chief Justice of the Federation, he worked with the Ministry of Justice, Ikeja, Lagos, Ogun State between 1978–1979, as the Pupil State Counsel. When he left Ministry of Justice, he went to partner in the Law firm of Effiom Ekong & Company, Calabar between 1979 – 1988. He later became the Principal Partner/Head of Chamber of Walter Onnoghen & Associates, Calabar from the period of 1988 – 1989. Between 1989 – 1998, he was a High Court Judge of Cross Rivers State Judiciary. During his time as the High Court Judge of Cross Rivers State Judiciary he was made the Chairman of Cross Rivers State Armed Robbery and Firm Arms Tribunal and he held the post for 3 years between 1990 – 1993. Sometime in 1996 while still holding the post of High Court Judge of Cross Rivers State Judiciary, he was appointed the Chairman, Judicial Enquiry into the Crisis between Students of the University of Calabar and Obufa Esuk Orok Community, Calabar. In 1998, he was the Chairman, Failed Bank Tribunal, Ibadan Zone. Between the period of 1992 to 2004, he served as the Judge, High Court of Rivers State while from 1998 to 2005 he served as the Justice of the Court of Appeal. In February 2016, Justice Onnoghen led a seven-man panel of Justices of the apex court who reviewed and upheld the death sentence of Chukwuemeka Ezeugo of the Christian Praying Assembly. In 2007, Justice Onnoghen played a huge role in 2007 election which saw the Late Umaru Yar’adua as President of the federal republic of Nigeria. He had a dissenting judgment that indeed annulled the presidential election. His position was however a minority judgment.
Onnoghen's trials started when a petition was filed by the civil rights group at the Code of Conduct Bureau alleging that he owns ” sundry accounts primarily funded through cash deposits made by himself up to as recently as 10 August 2016, which appear to have been run in a manner inconsistent with financial transparency and the code of conduct for public officials.” The allegations are listed . The trial commenced January 14, 2019 at Code of Conduct Tribunal but Onnoghen was absent. It was then adjourned to the following week because Onnoghen faulted the summons procedure. The next hearing was slated for January 22, 2019 but he failed to show up in court again. Following his absence again, President Muhammadu Buhari suspended him 26 January and appointed Tanko Ibrahim as acting Chief Justice of Nigeria. His office was thereafter sealed by the police and members of the National Interest Defenders and Lawyers protested at the entrance of the National Secretariat of the Nigerian Bar Association. His suspension caused a lot of uproar from political stakeholders, lawyers and even gained international prominence from International bodies. Atiku described his suspension as ‘Dictatorship Taken Too Far'. Minister of Information, Lai Mohammed, accused those criticizing President Buhari over Onnoghen suspension as hypocrites. On 28 January 2019, the Code of Conduct Tribunal adjourned his trial indefinitely.
Conviction as CJN
Walter Onnoghen was convicted by the Code of Conduct Tribunal on Thursday April 18, 2019 for false assets declaration, With o and he was unable to account for them. CCT rules that he is banned from holding public office for 10 years. President Buhari received Onoghen's voluntary resignation letter which is effective from May 28, 2019 After an initial opposition to Buhari's acceptance of Onoghen's retirement, the National Judicial Commission stated that Onnoghen's retirement was in Nigeria's best interest
