Njenga has worked in the community-based natural resource management field for two decades. During this time, he developed a deep network and understanding of community conservation in Kenya. His experience ranges from local-level implementation work to project design and management, land tenure governance research to organizational development, and from policy development to public service.

Prior to joining Maliasili, Njenga previously worked as a Minister for Water, Environment and Natural Resources for the County Government of Laikipia. In this role, he provided both strategic and operational leadership that led to more than 100,000 households accessing clean drinking water, and new policies and laws governing natural resource management at the county level. He also served at the leadership level at the Council of Governors caucus of county ministers in charge of natural resources management. Njenga has previously worked as the Executive Director for the Zeitz Foundation and also worked with Maliasili before as Kenya Portfolio Manager. He is a 2013 Kinship Conservation Leadership Fellow and a 2011 ESRI Society for Conservation GIS Scholar. He has degrees from Moi University and Durell Institute of Conservation and Ecology (DICE) at the University of Kent, Canterbury.