Delph’s move to City had appeared over after he “set the record straight” over his future.
City agreed to meet an £8m release clause inserted into the new four-and-a-half-year contract signed in January.
City boss Manuel Pellegrini said, “At just 25 years old, he still has his best years ahead,”
“I am looking forward to working with him,”He is an excellent player
He will wear Frank Lampard’s number 18 shirt from last season.
Aston Villa released a 30-word statementconfirming their captain’s exit.
“Aston Villa can confirm that Fabian Delph has exercised the release clause in his contract and will join Manchester City,” it said.
“We’d like to wish him success in his future career.”