The 25-year-old has penned a one-year deal with the Warriors and, subject to a medical, will join his new team-mates for pre-season training next week.
He joins from French ProD2 team Carcassonne and previously spent three seasons playing with the Pampas XV, competing in South Africa's Vodacom Cup.
Ascarate said: "This is a great move for me. I'm excited about the prospect of playing in the RaboDirect PRO12 and Heineken Cup with Glasgow next season.
"I should be able to settle in quickly after playing in Europe last season and then in the summer against England. I'm happy that I'll have a month of training with the squad before the new season gets under way, which will give me plenty of time to get to know my new team-mates.
"Glasgow have a lot of very good players including three British and Irish Lions, so it'll be difficult for me to get into the team, but I'll work hard to try and achieve great things with Glasgow."
Ascarate, who can play at inside or outside centre as well as at full-back, has eight caps for Argentina and recently featured for his country in the double-header against England.
Glasgow head coach Gregor Townsend said: "Since Peter Horne injured his knee, we've conducted a global search to find the ideal replacement for the start of the season.
"Gabriel can play in a number of positions in the backline, is very strong in defence and has an intelligent kicking game.
"He has played at a high level and most recently played at inside centre for Argentina in their second Test against England, so he should be in good condition for the new season.
"He will be an excellent addition to our squad, to help us compete in both the RaboDirect PRO12 and Heineken Cup next season."
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- Heineken Cup