Since Joshua joined university in August 2013 he started training seriously. He competed in national races and eventually represented his university at the World University Cross Country Championships where he took the gold medal. Joshua made his international debut at the TCS World 10k in Bangalore where he surprisingly took the second place behind World Half Marathon Champion Geoffrey Kamworor.
As the fastest athlete in the field, Joshua traveled to Eugene for the 2014 World Junior Championships. He lived up to the expectations and won the golden 10.000m medal for Uganda.
As a strong 10.000m athlete, Joshua wanted to break the Ugandan National Record over 10k in 2015. He chose the fast 10k course of Berlin to give it a try. After a slow start of the race, he pushed the pace in the second part of the race. He secured the win and set a new national record of 27:50!
After some time training in Kenya, Joshua went back to Uganda to train in Kapchorwa. He had a great start of 2016 by winning the Laredo 10k in a new national record of 27:46. Followed by a victory in the Carslbad 5k. He then moved his focus to the track for the rest of the year. Shanghai Diamond League 5000m was his first track race of the season. He took second in a new personal best of 13:00.60.
Joshua represented Uganda in the 10,000m and the 5000m at the Rio Olympics. He ran a strong 10,000m race and finished as number six in a new personal best of 27:10.06. One week later he finished 8th in the 5000m final.
At the 2017 London world Championships Cheptegei sprinted with Mo Farah to the finish line to just miss out on the gold medal during a standout race. The silver medal secured Joshua's place at the top for a long time to come.
In november of 2017 Joshua challenged the 15km world record at the Zevenheuvelenloop in Nijmegen, the Netherlands. In stormy conditions Cheptegei stayed only 3 seconds out from securing the world record.