Born in Mindelheim, Reimer and his younger brother Jochen started playing ice hockey at EV Bad Wörishofen, before joining the youth setup of ESV Kaufbeuren.

On 26 January 2012, Reimer agreed to leave Düsseldorfer EG at the season's end to join fellow DEL team Nürnberg Ice Tigers on a three-year contract.

He posted 42 points in 47 regular season games before ending his career in the pre-playoff round against the Fischtown Pinguins.

[8] On 21 February 2018, Reimer scored the overtime game-winning goal to defeat Sweden in the quarter-finals of the 2018 Winter Olympics in Pyeongchang, before capturing silver with Germany.

[9] After 105 caps for Germany (29 goals, 27 assists) and participating in five World Championships and the 2018 Winter Olympics, Reimer announced the end of his internationals career in April 2018.