The 33-year-old left Panathinaikos in January and has impressed over the past few months while on trial at the Sky Bet Championship club.
Samba told Villa's website: "I have enjoyed my time with Aston Villa and I am very pleased to continue this association after signing my contract with the club.
"I have played against Aston Villa many times and it's always been a club I have had the utmost respect for because of its standing in the game.
"I can't wait to put the shirt on this coming season. It's a big season as everyone knows and if I can play my part in making it successful, I will be very happy.