Malen joined Roma on loan from Villa in January and became an instant revelation for the Giallorossi with an eye-watering 15 goals in 20 appearances.
The Dutchman helped his side clinch a spot in next season's Champions League, with the Italian side confirming his £21.6 million arrival on Tuesday after triggering the obligation in his contract.
The 27-year-old, who only transferred from Borussia Dortmund to the Villans in 2024, has signed a four-year contract at Roma that expires in June 2030.
Malen will now look to repay that transfer fee in 2025/26 by continuing his ruthless scoring streak and helping them go deep into Europe's elite competition.
He was recently selected by Ronald Koeman for the Netherlands 2026 World Cup squad in North America, where he will look to fire his side to glory.