When his improved performances saw him set to be picked for the 2012 Biathlon World Championships, the DSV did not select him, escalating disputes between himself and the Association and eventually leading him to switch nationalities and apply for Belgian citizenship.

During this period, in order to rebuild his sporting career, he resigned from his position in the police force in Germany, and moved back in with his parents.

[5] He made his debut for Belgium at an IBU Cup meeting in Martell, Italy, in March 2014, taking two top 20 finishes in the sprint and pursuit there.

[7] After switching countries, in August 2014 he became the first Belgian biathlete to win a global title when he took the gold medal in the pursuit at the Summer Biathlon World Championships in Tyumen, Russia, having already taken a silver in the sprint the previous day.

[3][10] In January 2019, at the Oberhof World Cup meeting, Rösch announced that he would retire from competition after the next weekend's following World Cup round in Ruhpolding, explaining that he felt it was the right time to retire as he was expecting to become a father for the first time, with his girlfriend being due to give birth in March.