Makoun makes move to Olympiakos
Makoun, 28, joined Villa in January from Lyon on a three-and-a-half-year deal for an undisclosed fee but has been unable to hold down a regular first team place at Villa Park.
He was greeted by 250 fans outside the offices of the club's offices after being presented to the Greek media.
"I feel very good about the way the Olympiakos family have welcomed me," Makoun told reporters.
"I have come here to help this team grow even more and I am very happy about moving to this club, all that remains is to get down to work."
Olympiakos, the reigning champions, are yet to start their domestic season after their opening match against Kavala was among three games postponed because only 13 of the 16 teams have been confirmed to play in the top flight after a match-fixing scandal.
Ernesto Valverde's team will play in Group F in the Champions League alongside Arsenal, Marseille and Borussia Dortmund.