Alexis Miellet first competed in national junior championships in medium-distance races in 2012. He also starts in cross-country races, where he won the gold medal in the junior team classification at the European Championships in Belgrade in 2013 . There are also two other medals that he was able to win in the team or the mixed team in 2018 and 2019 .
In August 2018, Miellet competed at the European Championships in Berlin. As tenth of his preliminary run, he missed the semi-finals and finally finished 28th. A year later he also competed at the world championships in Doha over 1500 meters. Before that, he had set new records over the 800 and 1500 meters during the season. At the championships, he made it to the semi-finals as second in his preliminary run. In the first semifinal run, however, he was eliminated in eighth place and ended up in 17th place