Mwapachu was nominated for the post by Tanzanian President Jakaya Mrisho Kikwete. He was elected as Secretary General of the East African Community by the Summit of EAC Heads of State on April 4, 2006. Prior to this appointment, Mwapachu was Ambassador Extraordinary and Plenipotentiary and Tanzania's permanent delegate to UNESCO.
Mwapachu is a law graduate of the University of Dar es Salaam (degree obtained in 1969). He also holds a Postgraduate Diploma in International Law, International Institutions and Diplomacy from the Indian Academy of International Law and Diplomacy, New Delhi, India. The University of Dar es Salaam conferred on him a Doctor of Literature degree (Honoris Causa) in 2005.
Some of his posts prior to his appointment as the Secretary General of the EAC were:
Working with the Ministry of Local Government and Regional Administration in the 1970s.