In the 2017–18 season, Hornig competed regularly in the IBU Junior Cup, achieving his first top-10 result in Nové Město na Moravě.

At the Junior World Championships in Otepää, he won bronze in the sprint and silver with the relay, while finishing 12th in the individual race.

[2] He also claimed three medals at the Junior Summer Biathlon World Championships: gold in the men's relay, and bronze in the sprint and pursuit.

[3] At the Junior European Championships, he won gold in the individual race and silver in the sprint, becoming one of the most successful athletes of the event.

In the 2024–25 season, at the opening event in Kontiolahti, Finland, he achieved a new individual career best by finishing 15th in the mass start race.