[5] He made his Serie A debut on 24 August 2013, coming on as a late substitute in the opening game, a 2–1 away loss against newly promoted Hellas Verona.

[6][7] However, following the acquisition of Alessandro Matri in the late days of the summer transfer window, Milan decided they would let Petagna go out on loan to Sampdoria in order to gain more first team experience.

[9] In spite of that, the loan was terminated early and Petagna returned to Milan in January, having made five scoreless appearances during his stay at Sampdoria.

The side won the Viareggio Cup in February, defeating Anderlecht in the final, with Petagna scoring the equaliser for the rossoneri in a 3–1 win.

[18] On 12 August 2022, Petagna joined newly promoted Serie A side Monza, with an obligation for purchase if certain conditions are met.

[23] When Monza guaranteed survival in the Serie A, Petagna's obligation-to-buy clause was triggered, forcing the Lombardy club to permanently acquire the striker for a reported total cost of €14 million.

[24] On 30 August 2023, recently promoted to Serie A side Cagliari announced the signing of Petagna on a season-long loan from Monza, with an option to make the move permanent.

On 28 March 2017, Petagna made his senior international debut for the Italy national football team, along with four other players, coming on as a substitute in a 2–1 friendly away win against the Netherlands.