Born in Valjevo, Mladenović passed the youth school of OFK Beograd, and he was called to youth national selections as a member of a team from Karaburma. He moved to Kolubara in 2012 and that year he made 30 appearances, including 29 league and 1 cup match, and scored 1 goal.
Mladenović joined FK Metalac on the beginning of 2013. He made 13 Serbian First League appearances until the end of 2012–13 season. For the 2013–14 season, Mladenović made 18 league appearances with 2 goals, and also played in a cup match against Partizan and play-off match against Rad. In 2014–15 season, Mladenović was the most standard player, playing all season matches, he scored 3 goals on 30 Serbian First League appearances, and also had 2 cup appearances and 2 play-off matches against Napredak Kruševac, after then Metalac promoted in Serbian SuperLiga. Mladenović made his SuperLiga debut in the first fixture of 2015–16 season, against Partizan. Mladenović scored his first goal for the 2016–17 season in a match against Red Star Belgrade on 29 July 2016, 15 minutes after he replaced Milan Stojanović in second half of the match.
On 26 January 2017, Mladenović signed with Bodø/Glimt. Mladenović scored his first goal on a debut match for new team, in 5–0 victory over Elverum on 17 April 2017. Several days later, on 26 April, he also scored Norwegian Football Cup match against Fauske/Sprint. Making 6 appearances with 2 goals in both Norwegian domestic competitions, Mladenović terminated a contract with the club and left as a free agentat the beginning of August same year.
Mladenović returned to the Serbian side Zemun in summer 2017. He scored a goal and made an assist to Dejan Đenić on his debut match for 2–0 victory over Čukarički, after which he was elected for a player of the week in the Serbian SuperLiga. During the first half-season, Mladenović collected 18 matches at total in botn domestic competitions. In last days of December 2017, both sides mutually terminated the contract and Mladenović the club in the mid-season.
In late 2017, it was announced about Mladenović's moving to AEL. He officially promoted in new club on 3 January 2018, penning two-and-a-half year deal, along with fellow countryman Radomir Milosavljević and Bulgarian defender Hristofor Hubchev. Mladenović made his competitive debut for AEL on 14 January 2018, replacing Adnan Aganović in 3–1 defeat against Asteras Tripolis. Mladenović made his first start in 26th week of the 2017–18 Superleague Greece campaign, Apollon Smyrni. While with the club, Mladenović archived 11 league caps, mostly as a back-up, and also spent both of matches against PAS Giannina in quarterfinal of the Greek Football Cup as an unused substitution.
Returning to Serbia, Mladenović rejoined Zemun and started training with the club on 11 June 2018. Later, same month, Mladenović moved to Bačka Bačka Palanka and signed one-year contract with new club. Ending of November 2018, Mladenović mutually terminated the contract and left the club as a free agent.
