The 28-year-old has signed a one-year contract at Scotstoun, with the option for a second year, subject to visa and medical.
Niko last played for the Warriors in the club's 31-13 win over Munster in the 2014/15 Guinness PRO12 Final.
After signing for Glasgow in the summer of 2012, Niko established himself as a firm favourite amongst the supporters, crossing the whitewash 24 times in his 74 appearances for the club.
Niko was a key figure in the Warriors title-winning campaign in the 2014/15 season, scoring six tries in his sixteen appearances and providing valuable options due to his versatility, being able to play on the wing or at scrum-half.
His form in a Warriors shirt saw him named the club's McCrea Financial Services Player of the Season twice in three years.
Speaking to glasgowwarriors.org, Niko couldn't hide his delight at the move.
"It means so much to me," said Niko.
"Glasgow Warriors was my first professional club and first club outside of Fiji, and it’s where I met a lot of good people.
"Dave Rennie is a very good person. He's very down-to-earth and he had a good chat with me before I decided to come back. He's a good man.
"I always play like it's my last game and I'm really looking forward to playing in front of the fans again.
"I'm very excited to be back in Glasgow."
Glasgow Warriors Head Coach, Dave Rennie, added: "I've seen Niko play a lot of test footy for Fiji and for Glasgow Warriors, when they won the title too. He's a bit of a freak on the field, he’s a game breaker.
"I know he was incredibly popular here with the fans and when I met with him he made it very clear that he was very passionate about Glasgow and wanted to come back.
"We've got three really good nines already, Henry (Pyrgos) and Ali (Price) are Scotland internationals and George (Horne) has really impressed us in pre-season.
"Niko is going to have to work really hard, but the fact that he can play on the wing and at full-back is a bonus and his utility value will help us during the Autumn Tests and Six Nations periods.
"We want to harness his individual brilliance and not coach it out of him, he'll be dynamic on our artificial pitch.
"He's been out of footy for a fair amount of time, so the next month will be about getting his body right so that once he gets his opportunity he's ready to fire."