Although his parents never supported him to start running, Ghirmay Ghebreslassie chose for an international running career instead of joining university. His first international race representing Eritrea, were the World Junior Cross Country Championships in 2013, where he finished in seventh position. After running some track races in Europe, Ghirmay realized that he had more talent for the longer distances on the road and he moved up to the half marathon distances. He made his debut in Paderborn in 2013 where he took the lead after six kilometers. His competitors never saw him again as he went on to finish in a new course record of 60:09.
So far, Ghirmay ran some strong half marathons in 2014 finishing second at the National Championships, first in San Blas, first in Göteborg and seventh at the World Championships (in a World Junior Leading time of 60:10).
The next step for Ghirmay was pacing the 2014 Chicago marathon but after running 35k in 2:04 pace, he decided to finish the race and he became sixth in his debut marathon. He improved his personal best by more than one minute by finishing second at the 2015 Hamburg Marathon.
His time in Hamburg made him the fastest Eritrean in 2015 so he was asked to represent Eritrea at the World Championships in Beijing. Although he was not the favorite for the medals, he did not seem to have any problems with the hot conditions in Beijing. He left the other athletes behind after 35k and won the first ever gold medal for Eritrea at the World Championships.
In 2016, Ghirmay took two fourth places in the high quality fields of London marathon and the Rio Olympic Games. After 30 km in Rio he found himself in 13th position but he speeded up and almost closed the gap with the third place in the race. The year was not complete for him without a victory. He competed in the New York City marathon and won the race by a big margin. He became the fifth fastest athlete ever in New York, the youngest winner ever and the first Eritrean to win a World Major.