|Date of birth||16 July 1985|
|Place of birth||Čakovec, SR Croatia, Yugoslavia|
|Height||1.75 m (5 ft 9 in)|
|2018–2021||Polet Sv. Martin na Muri|
|*Club domestic league appearances and goals, correct as of 26 March 2023|
Mezga acquired Slovenian citizenship on 23 August 2012.
Coming from the village of Brezje, near Čakovec, in the region of Međimurje, Mezga went through the ranks of several lower-tier local clubs, debuting at the age of 15 for the seniors of NK Sloga Čakovec, before joining the under-17 team of NK Varteks. In his last season of eligibility for the under-19 team, he left the club, however, and joined the Croatian Second League side NK Čakovec, where he played for the next three years.
In 2007, Mezga joined Slovenian PrvaLiga side Maribor. He soon established himself in the first team and won his first league title with the team in 2009, and was also declared the most distinguished player of the season by the Maribor fans. Maribor went on to win four titles in the following five seasons, with Mezga featuring heavily in all campaigns, and was selected in the league's ideal eleven of the 2011–12 championship.
After his contract expired in the summer of 2014, Mezga joined Hajduk Split in his homeland. He briefly returned to Maribor in August 2016, before signing for Portuguese side Nacional in January 2017.
- "Dejan Mezga". worldfootball.net. Retrieved 27 March 2023.
- Austrian career stats – ÖFB
- "Mezga brez statusa tujca" [Mezga is not foreign player anymore] (in Slovenian). NK Maribor. Retrieved 1 September 2012.
- "Dejan Mezga iz Brezja potpisao za splitski Hajduk" (in Croatian). 12 August 2014. Archived from the original on 17 September 2016. Retrieved 2 June 2021.
- Biografija at dejan-mezga.com
- "Mezga Dejan". hnl-statistika.com (in Croatian). Archived from the original on 10 September 2012.
- "Vijol'čni bojevnik" [Purple Warrior] (in Slovenian). NK Maribor. Retrieved 16 October 2016.
- T. O. (14 May 2012). "Vršič najboljši igralec sezone slovenskega prvenstva" [Vrsic is the best player of the season] (in Slovenian). RTV Slovenija. Retrieved 16 October 2016.
- Dominko, Peter (26 January 2017). "Mezga še drugič v karieri zapustil Ljudski vrt" [Mezga left Ljudski vrt for the second time in career]. Slovenski nogometni portal (in Slovenian). Retrieved 26 January 2017.