Villa boss Dean Smith moved for Reina after the struggling Premier League club’s first-choice keeper Tom Heaton was ruled out for the rest of the campaign.
Heaton suffered a knee injury against Burnley on New Year’s Day and Jed Steer, who featured during Villa’s promotion from the Championship last season, is also out through injury.
“We’ve managed to secure a player in Pepe who has a wealth of Premier League experience,” Smith told Villa’s website.
“At the start of the summer we were looking for an experienced goalkeeper and brought in Tom Heaton.
“Unfortunately, his injury has ruled him out for the rest of the season but Pepe fits our criteria not just because of his experience but also because of his leadership qualities.”
Reina, who has been capped 36 times by Spain, made 394 appearances for Liverpool between 2005 and 2013 before moving to Bayern Munich after a loan spell with Italian club Napoli.
The 37-year-old could make his Villa debut in Saturday’s trip to Brighton.
With Orjan Nyland in goal, Villa were thrashed 6-1 by Manchester City on Sunday to slip into the Premier League relegation zone.
