In her youth, Sheila Chepkirui competed in age category competitions. She defeated Yuriko Kobayashi over 1500 m at the 2005 World Youth Championships in Athletics to claim her first international gold medal. Her finishing time of in a 4:12.29 minutes was a championship record.[1] She returned to defend her title two years later, but ended up as bronze medallist at the 2007 event.[2] She failed to improve at the 2008 World Junior Championships in Athletics and did not get past the heats. She dropped out of the sport after that year.[3]
In September 2022, she came close to the women-only 10 kilometres world record at the Brașov Running Festival in Brașov, Romania. With her time of 30:07 Chepkirui, who set her 29:46 personal best in a mixed race in Valencia in 2020, broke the Romanian all-comers's record by more than two minutes, and was only six seconds off the women-only world record.[11]
In November 2024, Chepkirui won the New York City Marathon's women's race, securing her first major marathon title with a time of 2:24:35.[12]