Weißhaidinger broke the Austrian under-23 shot put record in 2012, throwing 19.22 m. He was a finalist in both the shot and the discus at the 2013 European U23 Championships, but did not place in the top six in either event. Weißhaidinger first broke 60 metres with the men's 2 kg discus in 2014, throwing 60.02 m in April and 60.68 m in May; he was the first Austrian under-23 thrower to exceed 60 metres, breaking Gerhard Mayer's national under-23 record from 2001.