She started running in Spanish road races in 2004. She set a personal best of 71:19 minutes to win the 2005 Media Maratón Santa Pola and also won at the Granollers Half Marathon. She continued to compete at low level races and was runner-up at the 2007 Reims Half Marathon. She won that race the following year and improved her best at the Porto Half Marathon, running 70:43 minutes for third. She bettered that time at the 2009 Valladolid Half Marathon, taking the title with a run of 69:26 minutes, and was runner-up at the Porto race.[2] She made few competitive appearances over the following 18 months, but won the Zhuhai Half Marathon on her Asian debut in December 2011.[3]
She won the Kenya Defence Forces Cross Country title at the start of 2013,[9] then ran a personal best of 1:06:48 to win the Prague Half Marathon[10] – a time which brought her into the top 10 fastest women half-marathoner of all time. She won the national trial event for the 10,000 m and went on to take the silver medal behind Tirunesh Dibaba.[11] She ended the year with runner-up finishes at the BOclassic and the Delhi Half Marathon.[12]
In September 2015, in her second time competing at the marathon distance, she won the Berlin Marathon in 2:19:25[13] (a personal best by 38 seconds), which at the time made her the 7th fastest women marathoner of all time.[14]
Later in February 2016, Cherono finished the RAK Half Marathon in 1:06:07[15] (a personal best by 31 seconds), which at the time made her the 4th fastest women half-marathoner of all time.[16]
In 2017, Cherono won her second Berlin Marathon with a time of 2:20:23.[17] The following year, she won the Berlin Marathon for the third time with a time of 2:18:11 and set a course record.[18]
As of 2020[ref], Gladys Cherono is the 8th fastest women marathoner of all time[1] and the 24th fastest in the half-marathon distance.[19]