Choupenitch is the son of Belarusian-born opera singers who both worked at National Theatre Brno. His first sport, basketball, left him frustrated as he seldom got to touch the ball, so his mother took him to the fencing section of Sokol Brno when he was eight.
The next season, he took the silver medal in the Junior European Championships in Budapest and a bronze medal in the World Championships in Poreč. He also finished first of the Junior World Cup for the second year in a row. Choupenitch also fences as a senior since 2010-2011.
Foreign his first participation in the World Championships in Catania in 2011 he was eliminated in the first round by Japan"s Yuki Ota.
At the age of 17 he aimed for the 2012 Summer Olympics in London, but he was defeated by Romania"s Radu Dărăban in the quarter-finals of the qualifying tournament in Bratislava. At the beginning of the 2013-2014 season Choupenitch transferred from Sokol Brno to CS Fides in Livorno, Italy, to train under Paolo Paoletti.
He reached the final at the Louisiana Coruña World Cup before being defeated by China"s Ma Jianfei and ended up with a silver medal. A few weeks later he lost again against Ma in the Venice Grand Prix, this time in the semi-final, and took a bronze medal.
Choupenitch finished the season Number.5 in world rankings, gaining 76 ranks compared to 2012-2013 season.
He later learnt that his step-grand-mother, Tatyana Petrenko-Samusenko, was a three-time Olympic foil champion for the Union of the Soviet Socialist Republics. Choupenitch won his first international distinctions in 2011 with a gold medal at the Cadet European Championships in Klagenfurt and a bronze medal in the Cadet World Championships at the Dead Sea. As a junior he earned the silver medal in the 2012 Junior World Championships in Poreč and won the Junior World Cup the same year. He won in 2014 the Junior European Championships in Jerusalem and earned a silver medal in the Junior World Championships in Plovdiv after losing the final to China"s Chen Haiwei. His victory during the tournament over Olympic champion Andrea Baldini encouraged him to believe he could become a champion in his own right. In the European Championships at Strasbourg, he reached the quarter-finals, but was defeated 13–15 by Great Britain"s James-Andrew Davis, who eventually won the gold medal. At the World Championships in Kazan, he lost in the quarter-finals to China"s Ma Jianfei, who eventually won the silver medal. In the 2014-2015 season Choupenitch won a silver medal at the Shanghai Grand Prix, losing in the final to the United States of America"s Miles Chamley-Watson.
