In January 2008, he moved to Germany to play for Hertha BSC for a fee of €3 million, which made him the most expensive player that Vojvodina ever sold.

On 21 August 2010, Kačar debuted for Hamburger SV, coming on as a substitute for Eljero Elia in the 79th minute of a 2–1 home win against Schalke.

After an unsuccessful stint in Japan playing for Cerezo Osaka, on 19 July 2016, Kačar left Hamburg to join FC Augsburg.

On 7 September 2008, Kačar scored five goals for the Serbian U-21 team in an 8–0 demolition of Hungary in a qualifying match for the 2009 UEFA European Under-21 Football Championship.

[3] In June 2010, he was selected in Serbia's squad for the 2010 FIFA World Cup,[4] where he appeared in group stage match against Germany.