Appointed Judge of the High Court of Borno State, Nigeria in 1997 and Chief Judge in the year 2006. A member of the National Judicial Council of Nigeria, he is currently engaged in a major national judicial reform undertaking, as chairman of the National Judicial Council (NJC) Judicial Information Technology Policy Implementation Committee (JITCOM) that is in the process of automating court processes in Nigeria; sits on the National Judicial Council committee on the Implementation of Transparency and Anti-Corruption Policy and the Corruption Trials Monitoring Committee (COTRICOM).
Justice Zannah is Deputy President at the International Organisation for Judicial Training (IOJT) and sits on the boards of several international bodies in the field of law and justice, such as the International Society for the Reform of Criminal Law (ISRCL}, the Commonwealth Judicial Education Institute (CJEI) and the International Institute for Judicial Excellence (IIJE), The Hague.
He was awarded the Medal of the International Society for the Reform of Criminal Law (ISRCL} in 2012 and the United States National Centre for State Courts (NCSC) Distinguished Service Award in 2013.