The Scotstoun side have been without their first-choice No 10 Adam Hastings since the end of October after he suffered a shoulder injury playing for Scotland against Wales.
Pete Horne, who has been used at both 10 and 12 by Glasgow, is also out due to a head knock, while the club’s other senior fly-half, Brandon Thomson, has struggled with his form in recent weeks.
Ross Thompson impressed in the playmaker’s role in Saturday’s 23-22 win over Edinburgh in what his first start for Warriors. But Glasgow coach Danny Wilson has been looking for experienced cover at stand-off and will hope Keatley fills the bill.
The 33-year-old, who has played for Munster, Connacht and London Irish, was released by Benetton earlier this month.
Wilson said: “It’s apparent and appropriate to suggest that we need to add an experienced fly-half to our situation that we are currently in.
“In our last recruitment cycle, pre the season starting, we wanted to bring in both a 15 and a 10, however, we didn’t the opportunity to do that due to Covid.
“Pete Horne has done a great job for us at fly-half this season, however, 12 is his favoured position and with his recent concussion problems, and Adam Hastings’ shoulder, we need bring in some experience at fly-half for the last six months of the season.
“We now have that opportunity and we are chuffed to be able to bring in someone of Ian’s quality, experience and knowledge into the squad.”
Keatley was capped seven times by Ireland between 2009 and 2017. He is the Pro12/Pro14’s third highest scorer with 1,524 points over 13 years and only former Glasgow Warriors fly-half Dan Parks and Wales’ Dan Biggar can claim to have scored more.
“Ian Keatley has been a fantastic player over the years for Munster, Connacht and more recently at Benetton,” Wilson added.
“Ian’s experience will be great from a performance point of view. He will also be invaluable to the development of our young players, including the likes of Ross Thompson, and also enable us to look at Pete [Horne] in his natural position of inside centre.”
Keatley, who made 212 appearances in the Pro12/Pro14, left Benetton by mutual consent after struggling for game time recently with the Italian club.
He will look to reboot his career at Scotstoun and described the move as the chance for a “fresh slate”.
“It’s a strange time to be joining the team with everything that’s going on with Covid, however, I’m really happy to be joining a club and a city with a proud rugby history,” Keatley said.
“I’m looking forward to being able to start on a fresh slate with Glasgow and I’m excited to begin working with Danny and his coaching team.
“This club is a top quality outfit and I’m relishing the chance to be able to play alongside some of its top quality talent.”