The highly-rated 20-year-old, the younger brother of Reading player Leandro, has penned a three-year deal with the option of a fourth year.
Bacuna is seen as an agressive, technically accomplished player with good mobility who is capable of playing a holding role in the middle of the pitch or further forward.
He follows on from the club record signing of Holland defender Terence Kongolo and the additions of Egyptian winger Ramadan Sobhi and Leicester City goalkeeper Ben Hamer.
Huddersfield head coach David Wagner said: “I am delighted that we have 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 is a young, hungry player that has already played a lot of football for someone of his age and even if he is still very young, he strengthens our options in this position after we lost Dean Whitehead to retirement at the end of last season.”