[1] In October 2009 he refereed his first international senior match — a 2010 World Cup qualifier between Finland and Wales in Helsinki.

The same season also saw him referee a Romanian Liga I match between FC Politehnica Timișoara and Dinamo București on 23 November 2009.

[citation needed] In the UEFA Champions League, Mažić first appeared at the Camp Nou Stadium on 19 September 2012, refereeing Barcelona's 3–2 win over Spartak Moscow match.

In early April 2014, Mažić was selected as the referee of the Champions League quarter-final first leg match between Paris Saint-Germain and Chelsea at Parc des Princes.

[citation needed] Mažić refereed the Germany vs. Portugal group stage match in Salvador da Bahia.

[6] After the game, Iranian manager Carlos Queiroz, unsatisfied with the referee, was quoted saying: "Will this man be able to sleep tonight?

[9][10] Mažić later refereed the Europa League semi-final return leg in mid-May, his third time being involved in a match at this stage of competition, between Dnipro and Napoli that was played in Kyiv instead of Dnipropetrovsk due to the Ukrainian conflict.

In July 2015 Mažić got hired by the Egyptian FA to referee the country's biggest league derby between Cairo cross-town rivals Al Ahly and Zamalek.

In the next phase of the Cup, the Serbian team was appointed to run the Round of 16 match between Hungary and Belgium at the Stadium Municipal in Toulouse, which the Belgians won 4–0.

During the tournament, Mažić also worked as a fourth official twice, at the Poland vs Portugal and France vs Iceland quarter-final matches.

On 26 May 2018, Mažić and his assistants Milovan Ristić and Dalibor Đurđević refereed the 2018 UEFA Champions League Final between Liverpool and Real Madrid in Kyiv.

At the next phase, the Serbian team was appointed to officiate quarter-final match between Brazil and Belgium in Kazan on 6 July.