[3] Häfner began his handball career at hometown club TSB Schwäbisch Gmünd, before moving to 2.

Having switched to Frisch Auf Göppingen the following year, Häfner would spend four seasons playing for the Swabians, with whom he won the DHB-Pokal in 2011.

[8] Häfner won the silver medal with the German junior national team at the 2008 European Championships.

At the 2016 European Championships in Poland, he was called up for the last game of the main round (against Russia) after Steffen Weinhold was injured.

At the 2016 Olympic Games in Rio de Janeiro, he won the bronze medal with the German team.