The 5' 10" midfielder will join The Terriers on a three year deal that will run up until the summer of 2021, with the Club having the option for a further season.
Terriers boss David Wagner said: “I'm delighted that we've been able to bring Juninho in, especially before we report back as it allows him to have a full pre-season with the team.
“He's a young, hungry player that has already played a lot of football for someone of his age and even if he's still very young, he strengthens our options in this position after we lost Dean Whitehead to retirement at the end of last season.
“He's an exciting midfielder that offers all the aggression of a defensive midfielder and the technical skills and mobility of an offensive midfielder.
“We will give him all the support he needs to make the best out of the potential he definitely has."