He joins Glasgow from Sydney-based club side Eastern Suburbs for whom he played in the Shute Shield.
Tagive, 23, comes from a rugby league background but also had a spell with Super Rugby franchise, the ACT Brumbies.
He scored seven tries in ten appearances for Eastern Suburbs last season.
Tagive’s rugby league roots saw him play for NRL teams the Bulldogs and West Tigers.
He then moved to Canberra to study psychology and took up 15-a-side rugby at university. He was spotted by local clubs and then the Brumbies. He then went on to train with the Australia sevens squad.
He said he was pleased to be joining Glasgow, who are currently fourth in the Guinness Pro12.
“There is so much to be excited about, especially seeing how well the team has started the season,” Tagive told the Warriors website.
“My roots are in rugby league but I’ve spent a year at the Brumbies learning how to play union, surrounded by Wallabies and fantastic players and I’m really grateful to everyone there for everything they’ve done for me.
“[Former Glasgow winger] Taqele Naiyaravoro is a really good mate of mine, we were together at the West Tigers. He was nice enough to give me a call last week and give me a bit of advice on what to expect.
“He only had good things to say about his experience at Glasgow and that was really reassuring.
“One thing I’ve noticed about watching Glasgow Warriors is their play is a lot more expansive than I anticipated, so it’s really exciting and I can’t wait to get started.”
Tagive is 6ft 3in and over 100kg, and Glasgow coach Gregor Townsend believes he will add pace and power to his squad.
“Ratu is quick and powerful and arrives at a good time with Leonardo [Sarto] out for a few months through injury.” Townsend said.
“He has played at a good level in Australia and has shown that he has the ability to score tries and will help provide competition for places on the wing.
“I’m sure that he will develop within our environment and it won’t take him long to look to get to grips with the style of rugby we play.”