At the 2018 World Karate Championships in Madrid, Spain, he won the gold medal in the men's +84 kg event.

Horne won the gold medal in the men's kumite +80 kg event at the 2009 World Games held in Kaohsiung, Taiwan.

[6] In 2013, Horne represented Germany at the World Games held in Cali, Colombia and he won the gold medal in the men's kumite +84 kg event.

[8] Horne won the silver medal in the men's +84 kg event at the 2015 European Games held in Baku, Azerbaijan.

[12][13] In 2021, at the 2020 Summer Olympics while fighting Gogita Arkania in the men's +75 kg event, Horne broke his right arm leaving him unable to continue.