He joined the University of Dar es Salaam, Facalty of Education as Assistant Lecturer in 2003
He teaches different courses including Educational Psychology, Social Psychology,Psychology of adolescence, Introduction to Psychology, Psychology and Crime, Psychology of Human Development and Research Method.
Until his appointment as Permanent Secretary in the Ministry of Water and Irrigation, Professor Mkumbo was Principal of the Dar es Salaam University College of Education (DUCE) since March 2012. Earlier on, he had served as Head, Department of Educational Psychology and Curriculum Studies between July 2009 and June 2012, Associate Editor of Papers on education and development (PED) and examination officer at the University of Dar es Salaam School.
Professor Mkumbo has carried out research and published widely in Psychology and Education. He is also the author of different notable articles and books.