Christian Fassnacht became a professional player relatively late in life at age 22 however, his career to date has been very impressive.
He was signed by BSC Young Boys in 2017/18 season and helped the club to win its first championship title in 32 years by scoring 11 goals and providing seven assists. In 2020 they won the double for the first time since 1958. Also, in October 2018 he was able to play for the Swiss national team for the first time.
On 3 October 2019, Fassnacht scored a late goal deep into second-half stoppage time to give Young Boys a 2–1 home victory over Rangers in the Europa League group stage.
Fassnacht made his debut with the Swiss senior national team (he never represented Switzerland before at any level) in a 2–1 away loss against Belgium.