He played at the 2007 FIFA U-20 World Cup, reaching the final with the Czech team.

He spent time on loan at clubs including FK Ústí nad Labem and Slovácko in his early career.

He joined Sparta Prague on loan for the first half of the 2011–12 season, scoring twice in 12 matches.

[3] Mareš joined Dukla Prague in August 2013 on loan until the end of the 2013–14 season.

[5] Following his season on loan, Mareš signed permanently for the club in June 2014, agreeing a two-year contract.