A statement on Aston Villa's website said Cameroon international Jean II Makoun, 27, would be eligible to play for the club in around two weeks time once a work permit had been secured for the midfielder.
"I am thrilled to be here at Aston Villa," Makoun said. "I am really, really happy and very proud to have joined a great club. Villa have been after me for quite a while, so I'm delighted it's finally happened. I can't wait to get started," he added.
Villa boss Gerard Houllier said Makoun's versatility and experience would be an asset to the Birmingham club, who reportedly paid Lyon a £6 million transfer fee to secure the player's services.
"Jean is a player who can play in front of the defence as a sitter and defensive midfielder or as a box-to-box midfielder," Houllier said. "He has several assets in his game. He is also a very experienced player because he played Champions League football with Lille and Lyon."
Aston Villa face Birmingham in a derby match Sunday.