On 25th July 2023 Norwich City signed Swiss international winger Christian Fassnacht from Young Boys on a two year deal for an undisclosed fee. He reunited with David Wagner who was manager at Young Boys.

He began his professional career with Tuggen in 2014 for whom he made 18 appearances, scoring 11 goals. He moved onto Winterthur in 2015 for whom he played 50 games scoring 11 times. The following season was with FC Thun where he scored 10 goals in 36 appearances. He moved to Young Boys where he scored 72 goals in 241 appearances, and won the Swiss title in 2017/18, 2018/19, 2019/20, 2020/21 and 2022/23 as well as the Swiss Cup in 2019/20 and 2022/23.

He made his international debut for Switzerland against Belgium in 2108 and had 19 caps at the time of his move to Norwich, with four goals to his name (the first against Gibraltar in November 2019). He played in both the 2020 European Championships and the 2022 World Cup finals.

Fassnacht made his Norwich debut on 5th August 2023 in a 2-1 home win over Hull City on the opening day of the 2023/24 season, coming on as substitute. He scored his first Norwich goal in the 4-4 draw at Southampton on 12th August 2023. He made a total of 47 appearances in 2023/24, scoring six goals, as Norwich finished sixth reaching the Championship play-offs, before losing 4-0 to Leeds.

In October 2024 it was rumoured that Fassnacht was in talks with Young Boys over a return to them during the January 2025 transfer window. He had made just one appearance for Norwich in the 2024/25 season due to an Achilles injury and is out of contract at the end of the 2024/25 season. Respected Swiss outlet Berner Zeitung are reporting that Young Boys are interested in bringing Fassnacht back to the club after a poor start to their domestic season, having taken nine points from their opening 10 matches.

On 31st December 2024 he signed for Young Boys on a free transfer, but City have inserted player and club-related performance bonuses into the deal.  He played three times during 2024/25 to take his total to 50 appearances. Norwich manager Johannes Hoff Thorup said "Unfortunately for him and for us, he was not really a part of pre-season because of the injuries and he’s had several here in season also so it’s been difficult for him to be integrated with the squad and for me to see honestly what he could actually add to the squad. That’s unfortunate for everyone. Then, of course, because of his age and profile, he maybe isn’t the perfect fit for our strategy and the way that we want to go forward. When that option came on the table and he had the option to go back to Young Boys and it was a good contract for him with some more security for the next two or three years, we have to respect that and he wanted to accept that offer and go back. Based on all this, it’s a good solution for everyone.”  Fassnacht signed a contract until 2027 with Young Boys andthe move will be officially confirmed on 15th January 2025 when the Swiss transfer window opens. Fassnacht said: "I was able to fulfil my dream of playing abroad and will have very fond memories of my time at Norwich, even though I played fewer games than I had hoped this season due to injuries."