In the 2006–07 indoor season he ran the 800 metres in 1:46.91 minutes in Stuttgart. This was a Ugandan indoor record. He opened the outdoor season by winning the IAAF Grand Prix in Dakar. He also won the Grand Prix meet in Hengelo, and finished third at the Super Grand Prix meet in Doha, the Golden Spike Ostrava and the Bislett Games. Then, in July 2007 he achieved a new personal best time of 1:44.78 minutes at the Grand Prix meet in Athens. A fifth place at the All-Africa Games was followed by the entrance in the 2007 World Championships. Chepkirwok reached the final round, and in an unusually tight race, where all eight runners finished in the range of 1 minute 47 seconds, Chepkirwok finished fourth with 1:47.41. This was 0.02 seconds behind the bronze medalist, and 0.01 second ahead of the fifth placer. Rounding off the season, Chepkirwok finished seventh at the 2007 World Athletics Final.