He is set to join English Premiership side Worcester Warriors on a two-year deal.
Ofa joined Glasgow Warriors in September 2012 on a short-term contract, which was extended in January until the end of the current season.
He has so far made 11 appearances for the Warriors and played the full 80 minutes in the recent victory over Ulster at Scotstoun Stadium.
Glasgow Warriors head coach Gregor Townsend said: “We would like to thank Ofa for everything he has done for the club both on and off the pitch.
“He has fitted in really well in the short time that he has been here and this is fantastic move for him and his family.
“He is fully focused and committed to us until the end of the season and we are very happy that we’ll be able to call upon his services until then.”
Ofa Fainga'anuku said: “I’ve really enjoyed my time in Glasgow and I’d like to thank everyone at the club for their help and support.
“I am looking forward to being involved in the remaining games this season and contributing to what we hope will be a successful end to the campaign.”