Slafkovský won twelve medals at the ICF Canoe Slalom World Championships with ten golds (C1 team: 2003, 2009, 2010, 2011, 2013, 2014, 2015, 2017, 2018, 2019) and two silvers (C1: 2013, 2017). At the European Championships he won a total of 21 medals (12 golds, 6 silvers and 3 bronzes). Slafkovský also won the overall World Cup title in the C1 class in 2012, 2016 and 2018.