Jepchirchir ran track while at school and was spurred on by the achievements of Mary Keitany, who was a world half marathon champion at the time. She began to compete in road races in 2013, starting with two wins at 10K runs in South Africa, then a third-place finish at the Kisumu Marathon in her native Kenya, finishing the distance in 2:47:33 hours. She turned to cross country running at the start of 2014 and managed to take second place to Faith Kipyegon at the Kenyan Cross Country Championships – her first significant finish at national level. Her talent was spotted by Gianni Demadonna's team and she began to earn invitations to high level European road races. She won three straight races in France in late 2014, winning the Le Lion Half Marathon, the Marseille-Cassis Classique Internationale, then the Corrida de Houilles. She was narrowly runner-up to Janet Kisa at the end-of-year BOclassic 5K. She made her highest profile appearance yet at the 2015 London Marathon, but failed to build on her shorter distance achievements, as she could not finish the full marathon distance. However, she began to reach the peaks of road running in 10K and half marathon that year. Her best of 30:55 minutes at the Prague Grand Prix was the second fastest globally for the season and one week later she set a course record of 67:17 minutes to win the Ústí nad Labem Half Marathon – a time which placed her seventh on the year's top lists. She also defended her title in Marseille in October. Jepchirchir set a new best of 66:39 minutes at the 2016 Ras Al Khaimah Half Marathon. Despite the fast time, which moved her to 13th on the all-time lists, the strength in depth of the race left her in fourth some way behind winner Cynthia Cherotich Limo while six women ran quicker than 67 minutes. This performance earned her a place on the Kenyan team for the 2016 IAAF World Half Marathon Championships. The five-woman team led out the start of the race, with Ethiopia's Netsanet Gudeta and Genet Yalew also in contention. As the race progressed, this was whittled down to a Kenyan trio of Jepchirchir, Limo and Mary Wacera Ngugi, and this eventually resulted in a sprint finish between Limo and Jepchirchir. Despite having been among the least experienced and well-known of the Kenyan team, it was Jepchirchir who emerged as world champion, finishing the race in 67:31 minutes and leading the Kenyan women to the team title and a podium sweep with Limo and Ngugi. A course record came at the Yangzhou Jianzhen International Half Marathon in April, with her run of 67:21 minutes. At the 2017 RAK Half Marathon she broke two world records. She took three seconds off Florence Kiplagat's half marathon record in 65:06 minutes and set the 20K world record at 61:40 minutes. Her position as the world's best was short-lived, however, as Joyciline Jepkosgei broke both her world records the following month.
