Born in Prague, Vadlejch took part in international javelin competitions from a young age, reaching the finals at the 2007 World Youth Championships in Athletics, 2008 World Junior Championships in Athletics and the 2009 European Athletics Junior Championships. His senior debut followed at the 2010 European Athletics Championships, where he threw in qualifying only. He competed in the javelin throw at the 2012 Summer Olympics and placed 25th with a mark of 77.61 metres. He was eliminated in the qualifying round at the 2011 World Championships in Athletics, 2014 European Athletics Championships, and 2015 World Championships in Athletics.