Dzeko is Bosnia's most capped player and all-time top scorer. The 40-year-old is one of two survivors from his country's only previous World Cup appearance in 2014, alongside defender Sead Kolasinac.
Bosnia defeated Wales and Italy on penalties to come through the playoffs and Dzeko picked up a shoulder injury at the end of extra time against the Italians in the final and was unable to take part in the shootout.
Dzeko then missed four games for his club Schalke 04, but came off the bench in their last two fixtures to ease worries over his fitness for the World Cup, where Bosnia will face co-hosts Canada, Qatar and Switzerland in Group B.
Barbarez wasted no time in calling up Mahmic after the 21-year-old Austrian-born player had his request to change allegiance to Bosnia approved by FIFA earlier in May.
Mahmic featured for Austria at Under-17 and Under-21 level, and had also played with Bosnia's Under-19 team, and Barbarez already sees him having a long career with the national side.
"You can't believe how happy and proud he is to be with us," Barbarez told reporters.
"He plays in the position of eight and 10, he has depth, the profile of a player that we don't have much. A player who will continue to develop, with the aim that Bosnia will have good players in the next 10 years."
Kerim Alajbegovic may be the youngest in the squad, but the 18-year-old winger has already proven he has the skill and temperament for the big stage.
Alajbegovic came off the bench against Wales, set up Dzeko's equaliser and scored the winning penalty in the shootout and also converted a penalty when Bosnia beat Italy.
Bosnia play two warm-up matches against North Macedonia on May 29th in Sarajevo and Panama in St. Louis and begin their World Cup campaign against Canada on June 12th in Toronto.
Bosnia Squad
Goalkeepers: Nikola Vasilj (St Pauli), Martin Zlomislic (Rijeka), Osman Hadzikic (Slaven Belupo)
Defenders: Sead Kolasinac (Atalanta), Amar Dedic (Benfica), Nihad Mujakic (Gaziantep), Nikola Katic (Schalke 04), Tarik Muharemovic (Sassuolo), Stjepan Radeljic (Rijeka), Dennis Hadzikadunic (Sampdoria), Nidal Celik (Lens)
Midfielders: Amir Hadziahmetovic (Hull City), Ivan Sunjic (Pafos), Ivan Basic (Astana), Dzenis Burnic (Karlsruher SC), Ermin Mahmic (Slovan Liberec), Benjamin Tahirovic (Brondby), Amar Memic (Viktoria Plzen), Armin Gigovic (Young Boys), Kerim Alajbegovic (RB Salzburg), Esmir Bajraktarevic (PSV Eindhoven)
Forwards: Ermedin Demirovic (VfB Stuttgart), Jovo Lukic (Universitatea Cluj), Samed Bazdar (Jagiellonia Bialystok), Haris Tabakovic (Borussia Moenchengladbach), Edin Dzeko (Schalke 04)