The 29-year-old will join Gregor Townsend's squad this week, subject to a visa and medical, after leaving the USA Eagles sevens team following their Shield success at the Wellington Sevens in New Zealand.
The California-born player, who has scored 239 points in 21 sevens tournaments for his country, has been brought in to replace Gabriel Ascarate, who left the club last week after a neck injury ended his season.
Niua, who won his three full caps for the US last year, said: "I've played against Leone Nakarawa and Niko Matawalu on the sevens circuit and they're very good players and I enjoyed playing at Scotstoun with the USA sevens team at the Glasgow Sevens last year.
"I've been playing a lot of sevens recently, so I'm fit and ready to play games.
"It'll be the first time I've played for a club in Europe, but if things go well I'd love to stay in Glasgow beyond this season."
Head coach Townsend, whose team maintained their RaboDirect Pro12 top-four hopes with an 8-6 win over Connacht on Sunday, said: "Folau is an exciting player who has a lot of experience, having been a regular for the USA sevens team for the past few years and now with three caps for his full national team.
"He had a cracking game against the New Zealand Maori team at the end of last year and is a real ball-playing centre who is also a very effective ball carrier."