She started her career while at Kitopen Primary School. She finished 2nd at the Kenyan cross-country championships in 1991 behind Tegla Loroupe. Chepngeno was selected to compete at the 1991 IAAF World Cross Country Championships in Antwerp, Belgium, but finished only 46th.
In 1992 she won the Kenyan trails for the 1992 IAAF World Cross Country Championships. She finished 15th at the World Cross Country Championships held in Boston, United States and was part of the Kenyan gold-medal winning team.
She did not make the Kenyan team for the 1993 IAAF World Cross Country Championships, but won a bronze medal at the 1993 African Championships
The 1994 World Cross Country Championships were held in Budapest, Hungary where she became the first Kenyan woman to win individual World Cross Country Championships gold medal.
|1992||World Cross Country Championships||Boston, United States||15th||Long race|
|1993||African Championships||Durban, South Africa||3rd||3000 m|
|1994||World Cross Country Championships||Budapest, Hungary||1st||Long race|
- IAAF, March 20, 2007: A Kenyan XC legend - Helen Chepngeno
- Daily Nation January 31, 1999: Koech wins Armed Forces title again
- Daily Nation, February 05, 2007: Chepngeno, Kenya’s unsung athletics heroine 
- International Herald Tribune, March 28, 1994: Shooting for the Moon, Kenyans Win All but 1 Cross Country Gold
- IAAF, March 28, 2009: Senior Women’s Race Report - Amman 2009