Theuns made his debut for in 2014. He took his first victory in August 2014 in the
Grote Prijs Stad Zottegem. He also rode for his national team at the
2014 UCI Road World Championships. In 2015, he began his season with four top-ten finishes at the
Étoile de Bessèges, finishing fifth overall and winning the points classification. He took his second career win in March 2015 with victory in the
Ronde van Drenthe. In August 2015 it was announced that Theuns would join for the 2016 season. He was named in the start list for the
2016 Tour de France and the
2017 Vuelta a España. In 2018, Theuns signed with , before returning to ride for the following year. In 2019, he won the
Primus Classic. ==Major results==