The 24-year-old - who arrived in Glasgow over the weekend - arrives at Scotstoun following two seasons at New Zealand outfit North Harbour, competing for the Albany-based side in the second tier of the Bunnings NPC.
Standing at 6ft 5in and weighing in at 115kg, Fifita has prior experience of playing in the northern hemisphere; a highly-productive 2018/19 campaign saw him cross for 13 tries in 16 matches for El Salvador, helping the Spaniards to claim the Division de Honor title - the top tier of Spanish rugby.
Fifita made his international debut earlier in 2021, coming off the bench in Tonga's defeat to New Zealand in Auckland before earning a second cap against Samoa in a Rugby World Cup qualifier.
He will become the fifth Tongan - and first Tongan back - to represent Glasgow Warriors, following in the footsteps of Ofa Fainga'anuku, Sila Puafisi, Siua Halanukonuka and Fotu Lokotui.
Speaking on his first day at Scotstoun, Fifita told glasgowwarriors.org: "I'm pretty stoked to be sign for Glasgow and start this new chapter in my career.
"I can't wait to step out onto the field with these guys and I'm really happy.
"I'm really grateful for the opportunity and I want to thank both my agent and Glasgow for presenting me with it. Coming overseas was a big chance for me - I enjoyed my experience of it in the past when I was in Spain, and I'm looking forward to making more memories.
"I love to carry the ball and hopefully I can show the fans what I can do on the field."
Glasgow Warriors Head Coach Danny Wilson welcomed the winger, adding: "We're really excited to be able to bring Walter into our squad.
"He's a big, abrasive player who we believe can be a real asset to us out wide.
"We're looking forward to fully integrating him into our environment ahead of the next block of fixtures, and we're looking forward to seeing him perform in front of a packed out Scotstoun crowd."