The family soon returned to Vukovar where the youngster took up organized youth basketball at KK Borovo at age 5 but shortly following the war moved back to Serbia, settling in Bačka Palanka.

Before even getting an opportunity to play full squad basketball at FMP, Mačvan started turning heads via successful appearances at junior and cadet European and World championships as part of the Serbian national youth teams.

[4] Signing a four-year contract with Hemofarm on 18 December 2007, Mačvan joined a young squad featuring talented 19-year-olds Stefan Marković, Boban Marjanović, and Petar Despotović.

On 11 April 2009, 19-year-old Mačvan appeared at the 2009 Nike Hoop Summit game at Portland's Rose Garden alongside prospects such as Donatas Motiejūnas, Nikos Pappas, and Kevin Séraphin.

[18][19] Even before getting the first-team action on the club level with FMP, Mačvan began playing international competitions for Serbian national youth teams.

Coached by Slobodan Klipa, this time around, Mačvan's stats weren't as dominant as the duo of Miroslav Raduljica and Marko Kešelj took over the leading roles in the beginning stages of the tournament.

However, as the matches progressed, Mačvan started regaining top form and made a huge contribution in the final versus Lithuania, leading the team with 31 points.

In late summer 2009, coming off a great club season at Hemofarm as well as helping Serbia win the 2009 Universiade tournament on home soil in early July, Mačvan made the Serbian national team 12-man roster head coach Dušan Ivković took to EuroBasket 2009 in Poland.

Despite the player's youth and inexperience at the big stage, coach Ivković gave Mačvan decent minutes off the bench at his major tournament debut game versus world champions, Olympic silver medalists, and EuroBasket runners-up Spain that Serbia surprisingly won 66-57 while Mačvan contributed with 8 points and 3 rebounds in 17 minutes of action, hitting two clutch three-pointers in the third quarter,[20] incidentally his only field goals of the contest.

The group stage continued with a loss versus Slovenia and this time Mačvan got 18 minutes backing up Novica Veličković at the power forward position as his scoring output dropped off to 4 points.

In early June 2014, the national team's newly appointed head coach Saša Đorđević announced Mačvan alongside 28 other individuals on the preliminary list of players he was considering for the 12 final roster spots at the 2014 FIBA World Cup.

[22] On 1 July, announcing the official call-ups for the start of the training camp, Đorđević crossed out 9 names from the preliminary list including Mačvan's, saying the 24-year-old got excluded for tactical reasons while adding he had "an unfocused season [at Galatasaray] without a specific position".

We've been in constant contact before the call-up list had been announced and not once did he mention anything about an injury... More than anything else he owes an explanation to Duško Savanović and Milan Mačvan, two players that weren't called-up because I gave Veličković the advantage over them.

[24] In mid June 2016, shortly after getting a national team call-up ahead of the Olympic Qualifying Tournament, Mačvan broke his pinky toe, an injury that required a cast.

[citation needed] Mačvan represented Serbia at the 2016 Summer Olympics where they won the silver medal, after losing to the United States in the final game with 96–66.