In 2000, Sedlak won Yugoslav Youth Chess Championship in U18 age group.

In 2001, he won silver medal in Yugoslav Junior Chess Championship in U20 age group.

[1] In 2014, Sedlak won bronze medal in Serbian Chess Championship.

[2] Sedlak is winner of many international chess tournaments, including winning or sharing first place in Budapest (1999), Pula (2003), North Sea Cup in Esbjerg (2004), Subotica (2005), Zadar (2007), Boris Kostić memorial in Vršac (2008), Sarajevo (2009).

Sedlak played for Yugoslavia and Serbia in the Chess Olympiad:[3] Sedlak played for Yugoslavia and Serbia in the European Team Chess Championships:[5] In 2000, he was awarded the FIDE International Master (IM) title and received the FIDE Grandmaster (GM) title three years later.