|Born||April 10, 1965|
|4 (1987, 1996, 2012, 2014)|
|4 (1985, 1990, 2011, 2013)|
Jahr was the skip of the German team at the 1984 World Junior Curling Championships, where he led the team to a 7th-place finish. After juniors, he was picked up by the Rodger Gustaf Schmidt rink to play second for him. It was as a member of the Schmidt rink that Jahr won a gold medal at the 1985 European Curling Championships and a silver medal at the 1987 Hexagon World Men's Curling Championship. The team represented Germany at the 1990 European Curling Championship as well, but placed tenth.
Jahr would later leave the Schmidt rink to form his own team. He skipped the German rink to a 9th place at the 1996 Ford World Men's Curling Championship and a 7th-place finish at the 2011 European Curling Championships. He skipped Germany at the 2012 World Men's Curling Championship to an 11th-place finish. Jahr then led Germany to an 11th-place finish at the 2013 European Curling Championships.
Germany's poor performances in recent World Championships failed to automatically qualify the nation for the 2014 Winter Olympics. However, Jahr led Germany to a surprising win at the Olympic qualifying tournament, giving the team a berth at the Olympics. At the Games, Jahr led Germany to a 10th-place finish, with a 1–8 record. Jahr also played at the 2014 World Men's Curling Championship, where Germany finished in eighth place with a 5–6 win-loss record. Jahr announced his retirement from international curling at the conclusion of the round robin at the World Championship.
Jahr is a millionaire, as he owns part of the German publishing company Gruner + Jahr which was co-founded by his grandfather. Jahr also owns a real estate company and is a shareholder in a couple of casinos. He took time off from curling beginning in the late 1990s to focus on his business interests.