Antonsen started his career in badminton at six years of age in Kastanievej,
Viby. Together with his brother
Kasper Antonsen, they learned from his father who worked at one of the badminton clubs in Aarhus called AB. He made his international debut at the 2013 Forza Denmark International tournament. In 2015, he won the
European Junior Championship, defeating German player
Max Weißkirchen with a score of 21–9, 15–21, 21–9 in the final. In the same year, he also won several tournaments such as
Dutch International,
Belgian International, and
Irish Open, and awarded the 2015 European Young Player of the Year. In 2016, he won his first Grand Prix, the
Scottish Open Grand Prix. In the same year, he also won several other tournaments such as the
Spanish International,
Austrian Open, and
Swedish Master. In 2017, he won the silver medal at the
European Championship after being defeated by
Rajiv Ouseph of England with a tight score of 19–21, 19–21. He also reached the semi-finals in two
Superseries tournaments, the
2017 French Open where he lost to
Kenta Nishimoto from Japan with a score of 17–21, 15–21, and later the
Hong Kong Open where he was defeated by 2016 Rio Olympics gold medal winner
Chen Long from China with a score of 14–21, 21–19, 17–21. In 2018, Antonsen was chosen to be part of the Danish
Thomas Cup team and won a bronze medal. At the
Denmark Open Super 750 tournament, he managed to reach the semi-finals but was defeated at that stage by Chinese Taipei player
Chou Tien-chen with a score of 21–19, 11–21, 12–21. Play for the Aarhus AB, Antonsen won the
National Championships title three times in a row from 2017–2019. He won the
BWF World Tour title at the
2019 Indonesia Masters, defeating 2018 World Champion and then World number 1
Kento Momota from Japan in the final with a score of 21–16, 14–21, 21–16. He emerged as the men's singles champion and took the gold medal at the
2019 Minsk European Games beat
Brice Leverdez of France in the final with the score 21–19, 14–21, 21–10. At the
2019 Indonesia Open a Super 1000 tournament, Antonsen managed to step into the final round but he had to be satisfied as runner-up after losing to Chou Tien-chen with a score of 18–21, 26–24, 15–21. Antonsen captured the silver medal at the
2019 World Championships in Basel, Switzerland, lost to the first seeded, the reigning champion
Kento Momota in straight games 9–21, 3–21. Antonsen won the end of the season
2020 BWF World Tour Finals beating
Viktor Axelsen in the finals. In 2021, Antonsen participated at the
European Mixed Team Championships in Finland, and helped the team win the gold medal. At the May
European Championships, he was crowned as the men's singles champion, after organizers decided to cancel the finals, due to his opponent,
Viktor Axelsen, tested positive for COVID-19. Antonsen clinched a bronze medal after he lost in the semifinals of the
2021 World Championships to
Loh Kean Yew, the eventual World Champion, in straight games, 21–23, 14–21. Starting off the season in 2022, Antonsen managed to avenge his loss to Loh Kean Yew in the World Championships semi-finals, winning against the reigning world champion in the first round of the
All England Open, in rubber games, 21–15, 18–21, 21–13. He then lost in the next round to
Lakshya Sen, in straight games, 16–21, 18–21. On 30 April, Antonsen won silver at the
European Championships losing to compatriot Viktor Axelsen (17–21, 15–21) in the finals in
Madrid, Spain. Antonsen was very upset over the quality of his own play, saying audiences nearly deserved an apology. Antonsen then pulled out of the Asian leg of tournaments, the Indonesia Masters, the Indonesia Open, the Malaysian Open, the Malaysian Masters and the Singapore Open, citing injuries. In 2024, Antonsen managed to claim four BWF World Tour title, including his first ever Super 1000 event, in the
Malaysia Open, beating
Shi Yuqi in the final. Two week after his victory in the Malaysia, he won the
Indonesia Masters beating Brian Yang in the final. In April, he crowned as European champions by winning his second
European Championships title. At the
Indonesia Open finals in June, the "Istora boy" was beaten by Shi Yuqi in rubber game. Antonsen made his second appearance at the Olympics in the
2024 Paris Olympics, but his journey was stopped in the quarter-finals. On 24 August 2024, Antonsen announced on his social media that his coaching agreement with
Joachim Persson had been terminated as Persson was seen placing bets on matches. Since then, he appointed his brother
Kasper Antonsen, as his new head coach starting from October. He won the home soil
Denmark Open title, beating Koki Watanabe in the final in straight game. He then captured his fourth World Tour title of the year in the
China Masters. Antonsen qualified to compete in the year-end finals tournament the
BWF World Tour Finals, and finished runners-up to Shi Yuqi. He concluded the season as World number 2 in the BWF World ranking. Antonsen opened the 2025 season by competing in the
Malaysia Open. As a title holder, he unable to defend his title to last year finalist Shi Yuqi, losing the final match in straight games. After several early exits, Antonsen reached his second final in
Thailand Open but lost the match against home favourite,
Kunlavut Vitidsarn. In June, Antonsen beat Shi Yuqi in the semifinals of
Indonesia Open and won against Chou Tien Chen again in the final, repeating the feat he did back in 2019. Later on the year, Antonsen made the final in
Korea Open and won his second title of the year in
French Open. == Personal life ==