Fajdek represented Poland at the 2008 World Junior Championships in Bydgoszcz, finishing just off the podium in 4th despite throwing a new Polish junior record of 75.31 metres with the 6 kg under-20 implement. In 2009, his first year as a senior, Fajdek placed 8th at the European U23 Championships in Kaunas, Lithuania with a throw of 68.70 metres. Fajdek placed 3rd at the Polish Championships that year with a mark of 70.86, behind former Olympic and World Champion Szymon Ziółkowski and a returning Wojciech Kondratowicz.
In 2010 he grabbed another national bronze, this time with a throw of 73.85 metres.
Later that year, he improved his personal best to 76.07, good enough for 35th in the world. Fajdek continued to improve in 2011, finishing second at the European Team Championships in Stockholm with a new personal best of 76.98 metres.
He also dominated his speciality at the World University Games in Shenzhen, winning the gold with 78.14, more than four metres ahead of silver medallist Marcel Lomnický. A week later at the World Championships in Daegu, however, he only managed 75.20 and finished eleventh.
Fajdek first broke 80 metres at the Ostrava Golden Spike meeting in May 2012, finishing second to Hungary"s World silver medallist Krisztián Pars.
In his next competition at Montreuil he threw yet another personal best of 81.39, this time beating Pars. Fajdek is currently coached by Czesław Cybulski, who has also coached Ziółkowski and Anita Włodarczyk.