Having made his senior national team debut in 2007, Kadlec has scored eight goals in 67 caps for the Czech Republic, representing the country at three UEFA European Championships between 2008 and 2016.

[citation needed] When Kadlec's father signed for FK Drnovice in 1998, his son returned to the Czech Republic.

[5] On 17 November 2007, Kadlec was called up to the Czech national team in a UEFA Euro 2008 qualifying against Slovakia, and debuted in a 3–1 victory where he scored an own goal.

[7] On 16 June 2012, against Poland in the European Championship, Kadlec headed a ball off the line in the dying seconds, preserving the Czechs' spot in the quarter-finals of the tournament.

[8] The striker had beaten goalkeeper Petr Čech and appeared to be headed to the inside of the far post; if it had been scored, Poland would ensure a draw, and the Czech Republic would be eliminated from the tournament.