A relative late-comer to the sport, he made his first impact in the 2013 season at the age of 23. He won the 800 m at the Meeting Grand Prix IAAF de Dakar, setting a personal best of 1:45.40 minutes.[1] In his first race in Europe, he went under one minute and 45 seconds for the first time to take fourth at the Golden Spike Ostrava.[2] He placed a narrow second to Anthony Chemut at the Kenyan trials in July, improving further to 1:44.38 minutes.[3] This led to his selection for the 2013 World Championships in Athletics.[4] At the competition, he progressed to the semi-final and initially placed fifth but was disqualified for a lane infringement.[5] He ended the year with two performances on the 2013 IAAF Diamond League circuit, coming third at both the Weltklasse Zürich and the Memorial Van Damme.[6] The latter race was the fastest in the year, and Rotich's time of 1:43.22 minutes ranked him as the third fastest in the world that season,[7] making it a rapid rise for the athlete who was unranked in 2012.[8]