Fainga'anuku will give head coach Gregor Townsend a welcome additional propping option, with Jon Welsh (shoulder) and Ed Kalman (back) both having sustained long-term injuries.
Fainga'anuku, who is expected to arrive in Glasgow by the start of next week, starred for Tonga in their recent Pacific Nations Cup clash with Fiji, making the most of the opportunity to start in a position where Northampton Saints' Soane Tonga'uiha and Perpignan favourite Sona Taumalolo are also competing for the jersey.
The 29-year-old grew up playing rugby league, but switched to union in his late teens and was picked up by the Waratahs.
He has twice toured the northern hemisphere with Tonga, and is currently part of the prestigious Eastern Suburbs club in Sydney.
Townsend told www.glasgowwarriors.org: "We're very pleased to have signed Ofa Fainga'anuku and look forward to welcoming him to Glasgow in due course.
"We're delighted to be able to bring on board a man with Test experience to give more depth to an area where we have two long-term injuries.
"Having spoken to coaches who have worked with him, and studied his game on video, it's obvious that Ofa is a quality scrummager and tackler who works hard around the pitch.
"We'll be giving him the necessary support to settle in quickly and hit the ground running in what is a very important phase of the season."
Another new recruit, Fiji scrum-half Niko Matawalu, has now obtained a visa and is expected in Glasgow shortly.
Josh Strauss, the star South African No.8 signed last Tuesday, will also be arriving shortly.
OFA FAINGA'ANUKU
Date of Birth: 5 December 1982
Height: 1.83m
Weight: 118kg
International honours: Tonga (2 caps)
Previous clubs/regions: Waratahs, Eastern Suburbs
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