The 42-year-old former Manchester United midfielder, also the deputy to Republic manager Martin O’Neill, will work alongside Villa boss Paul Lambert as they try to revive the fortunes of the Birmingham club after a prolonged battle against relegation last season.
“I am delighted to be joining Aston Villa and I look forward to what promises to be an exciting challenge,” Keane said.
He added: “I am grateful to both Villa and the Football Association of Ireland for making this happen, and I would like also to thank Martin O’Neill.
“I am relishing the prospect of linking up with Paul Lambert and combining both roles to the full advantage of both Villa and Ireland.”
Keane’s arrival at Villa Park will bolster a backroom staff where former assistant manager Ian Culverhouse and football operations manager Gary Karsa were both sacked fore unspecified disciplinary reasons earlier this year.
Lambert insisted he was delighted to have former Sunderland and Ipswich manager Keane on board.
“Roy has a great knowledge of football, on the coaching side as well, and he’ll be a great asset and a big help to everybody here at Aston Villa Football Club,” Lambert said.
“As a player, he was one of the most accomplished in the history of the Barclays Premier League, and he’s brought that experience gained over many years into his career in coaching and management. The players will love working with him.
“Although we never played together, we competed against one another and he’s someone for whom I have a lot of time and respect,” the former Scotland midfielder added.
“He has worked under some great managers, some of the most successful in the game, and he’ll be a great help to myself as well,” he added in a reference to the time Keane spent under Brian Clough at Nottingham Forest and Alex Ferguson at United.
O’Neill brought Keane back into the game from the world of television punditry by giving him the Republic coaching role in November last year.
Former Villa manager O’Neill, who quit the club in 2010 over a dispute regarding transfer funds, said he had no problems with Keane joining the club after his assistant had been linked with the then managerial vacancy at Celtic — the Glasgow giants whom Keane briefly played for and O’Neill managed from 2000 to 2005.
“This is a good arrangement for us that allows Roy to remain in position as my assistant manager,” O’Neill said.
“Since he started in November, Roy has been excellent with the players and I have no doubt that he will bring all of the positive attributes he has shown here to the role he takes on at Aston Villa with Paul Lambert.”
Villa remain up for sale after US-based owner Randy Lerner said in May he wanted to cut his ties with the club after they finished 15th in the Premier League, just five points above the relegation places.