The package is structured as a £25m guaranteed fee with a further £5m in add-ons, and comes after Southampton stood firm through two rejected Aston Villa bids before finally accepting a figure close to their valuation.
The 24-year-old, who married Roy Keane's daughter Leah earlier this summer, has been left out of Southampton's matchday squad for their last three fixtures as the move gathered pace, a clear sign the south-coast club had already accepted his departure.
Harwood-Bellis progressed through Manchester City's academy before loan spells at Anderlecht and Burnley preceded a permanent switch to Southampton, where his deal turned permanent and he went on to make 134 appearances, scoring 12 goals and adding seven assists.
He earned his first England cap in November 2024 and represented his country regularly at age-group level, and his performances stood out even as Southampton suffered a dismal relegation from the Premier League in 2025.
The signing addresses one of the more pressing needs in Unai Emery's squad, with Villa having lost Morgan Rogers, Konsa and Ollie Watkins already this summer as the club continues an extensive summer rebuild.
Villa see Harwood-Bellis as more than capable of making the step back up to the top flight, and his versatility and experience should offer Emery a reliable option at centre-back. The move also continues an unlikely footballing subplot: Harwood-Bellis's father-in-law Keane, once a fierce Manchester United captain, now has a personal stake in how his son-in-law fares in the Midlands.
Villa had also considered alternatives including Club Brugge's Joel Ordóñez, AC Milan's Fikayo Tomori and West Ham's Jean-Clair Todibo before settling on Harwood-Bellis, whose age and upside made him the preferred option once Southampton's asking price was met.