Onnoghen was facing six charges of non-declaration and fraudulent declaration of assets relating to his failure to declare a series of bank accounts, denominated in local and foreign currencies, as required by law.
The Justice Danladi Umar-led tribunal found him guilty of failing to declare five bank accounts listed on the charge sheet during its ruling on Thursday, April 18, 2019.
The three-member panel ruled that Onnoghen acquired the undeclared funds fraudulently since he could not provide a satisfying explanation for the source. Monies found in the affected bank accounts were confiscated and forfeited to the Federal Government.
"The money in the five accounts which the defendant has failed to declare and disclose its source is hereby confiscated, seized and forfeited to the Federal Government of Nigeria as the money was acquired illegally and the defendant has failed to adduce any evidence how he acquired the money," Umar ruled.
The tribunal removed him as the Chief Justice of Nigeria, Chairman of the National Judicial Council (NJC) and Chairman of the Federal Judicial Service Commission.
He was also banned from holding public office in the country for the next 10 years.
Before delivering its judgement on Thursday, the tribunal also dismissed two separate motions filed by Onnoghen challenging its jurisdiction to entertain the case, and another asking Umar to recuse himself on the grounds that he had been charged with bribe-taking.
Umar said the tribunal has jurisdiction to try Onnoghen as a public officer, not necessarily as a judicial officer whose case has to be first entertained by the NJC like the judge's legal team argued.
He also said he didn't need to withdraw from the case since he was already absolved of the allegation of demanding bribe from a defendant.
President Muhammadu Buhari controversially suspended Onnoghen as CJN shortly after he was first arraigned in January 2019 and inaugurated Justice Tanko Mohammed as the acting CJN based on an order of the CCT, a move that attracted outrage from opposition parties and the international community.
Onnoghen turned in his resignation letter to President Buhari on April 4 after the NJC reportedly recommended his compulsory retirement due to alleged misconduct based on petitions filed by the Economic and Financial Crimes Commission (EFCC).
After the reading of the judgement on Thursday, Onnoghen's lead counsel, Okon Efut, hinted that an appeal will be filed and might be pursued all the way to the Supreme Court.
"We know that all is not over in this matter. The wheel of justice grinds slowly. It grinds slowly but surely. But this is not a matter that will end here.
"We shall avail ourselves of all the processes and the hierarchy of the judiciary," he said.
He also described the judgement as unconstitutional, alleging that it was already decided when the tribunal ordered Onnoghen's suspension without fair hearing in January.
He said, "This is an erosion of the fundamental principles of our Constitution and until some questions are answered, for instance, why is it that the due course of justice was not allowed to flow?"
Onnoghen, 68, was nominated as the Chief Justice by Vice President Yemi Osinbajo, as Acting President, in February 2017 and was sworn in on March 7, 2017.