She has a personal best of 2:27:38 hours for the longer distance (set in 2009) and was the 2013 winner of the Eindhoven Marathon.

Wanjiru spent her early career in Japan, running for Hitachi, then Second Wind AC and regularly competed on the road circuit there.

Wanjiru gained an athletic scholarship in Japan at Sendai Ikue High School (renowned for sports) as a teenager and moved there to study and improve her running.

[2] Initially she focused on middle- and long-distance track running; in her first year in Japan she won the high school title over 3000 metres.

She began that year with a significant personal best at the Osaka Ladies Marathon, running 2:27:38 hours for seventh place in a competitive field[11] At the final edition of the Yokohama International Women's Ekiden she helped the Kenyan women to second place behind the Japanese.