Dušan Vlahović was born on 28 January 2000 in Belgrade, FR Yugoslavia. Vlahović started playing football in "Altina Zemun" football school. Later he was with OFK Beograd for three months, and also made 1 appearance for Red Star Belgrade, but he joined Partizan in summer 2014 and signed his first professional contract with Partizan in 2015, when he was only 15 years old. At the beginning of 2016, Vlahović joined the first team and made his Serbian SuperLiga debut on 21 February 2016 against OFK Beograd, as the youngest debutant in history of Partizan. In the next fixture, played on 27 February 2016, Vlahović became the youngest player in the Eternal derby, when he was substituted on for the beginning of the second half. On 2 April 2016, Vlahović scored his first goal for Partizan against Radnik Surdulica in 3–2 home win and became the youngest scorer in club history. In summer 2017, Vlahović preliminary signed a five-year professional contract with Fiorentina, which became official on his 18 birthday, 28 January 2018.