The former Everton and Chelsea midfielder returns to Villa on a permanent basis from relegated Luton after making 24 appearances for the Birmingham club during a 2020/21 loan spell.
"Aston Villa is delighted to announce the signing of Ross Barkley from Luton Town," said a club statement, which did not disclose the length of the player's contract or a transfer fee.
The 30-year-old's arrival at Villa Park came after the club announced earlier Monday they had signed the Juventus duo of Samuel Iling-Junior and Enzo Barrenechea for a combined 22 million euros (£18.6 million, $23.6 million).
The Italian club said English forward Iling-Junior, 20, had joined for a fee of 14 million euros plus three million euros in possible add-ons.
Argentine midfielder Barrenechea, 23, has been signed for eight million euros plus three million euros in add-ons.
The pair joined the day after it was announced Douglas Luiz was making the reverse trip from Birmingham to Turin, the Brazil midfielder leaving Villa to sign a five-year deal with Juventus worth a reported £42.3 million.
Barrenechea started his career in Argentina before moving to Swiss club Sion.
London-born defender Iling-Junior came through Chelsea's academy before representing England at Under-21 level.
Villa finished fourth in the Premier League last season as the 1982 European Cup winners qualified for the Champions League.
But Villa's need to comply with the Premier League's Profit and Sustainability Rules (PSR) led manager Unai Emery to agree to Luiz's sale.
PSR rules permit losses of up to £105 million over three years.
Villa have already sold Tim Iroegbunam to Everton for £9 million during the close-season, while Chelsea paid £19 million for Omari Kellyman.
