Education
Ryutsu Keizai University.
Ryutsu Keizai University.
Njenga turned to marathon running and made his debut in 1999 at the Mombasa Marathon, taking fourth place, and then coming tenth at the Fukuoka Marathon. His breakthrough year came in 2002 when he was the runner-up at the Beppu-Oita Marathon and Chicago Marathon. His time of 2:06:16 hours in Chicago made him the third fastest runner in the world for 2002, behind only Khalid Khannouchi and Paul Tergat.
He is known for his consistent, close finishes in the Chicago Marathon, finishing as runner-up three times and third on two occasions, between 2003 and 2007.
Njenga is a featured subject in the 2007 marathon documentary Spirit of the Marathon. Njenga was victorious at the 2009 Hokkaido Marathon and took consecutive runner-up spots at the Beppu-Ōita Marathon in 2010 and 2011.