Finkler joins Victory from ABC Futebol Clube after he was loaned out by Criciuma, a team in Brazil's second division.
While the attacking midfielder has spent the majority of his professional career in Brazil, he spent the 2006-07 season at English Championship side Wolverhampton Wanderers.
New Melbourne Victory coach Ange Postecoglou said Finkler would bring flair to the group.
"Guilherme is an exciting prospect and I'm looking forward to working with him," Postecoglou said
"Brazilian players have certain qualities that not many other players possess so I'm confident he can bring a different type of flair to the group.
"More importantly he comes with a determination and ambition to be part of a successful team."
Finkler is expected to arrive in early July.
He joins Jonathan Bru, Spase Dilevski, Sam Gallagher and Adama Traore as Melbourne Victory's newest additions.