The striker, who in 2010 became the youngest-ever goalscorer for the Czech Republic national team, joins Eintracht on a four-year deal. His entire career has hitherto been spent in the Czech capital, transferring from the Prague Bohemians youth team to the most successful Czech side ever, Sparta, in 2008.
The striker represented Sparta in 146 games from 2008-2013 and scored 39 goals in the process. He also has continental experience in the UEFA Champions League and UEFA Europa League, which should prove extremely beneficial to a Frankfurt side who will juggle the Europa League alongside league commitments this term.
Sporting Director Bruno Hübner said that Kadlec was Coach Armin Veh's "top priority" and added that the club were delighted to have signed a player with "huge potential to develop".
The signing will come as a timely boost to Veh's men, who are currently sitting bottom of the Bundesliga table, having lost their opening two games of the season, scoring only one goal.