The 27-year-old Premiership forward has signed a one-year deal after spending the previous seven seasons with the North Queensland Cowboys.
Asiata played 128 NRL games for the Cowboys, including winning the 2015 Grand Final.
“John brings experience, some grunt and a heap of skill on the football field – he has been a player in demand,” said Broncos CEO Paul White on the club website.
“But what attracted us to him even more was his attitude and leadership off the field.
“To be chosen as the best clubman from your team not once but twice in five years shows John has the character and qualities we want around our footy club.
“He will add plenty to the Broncos on the field and just as much in the locker room and around the club – we are really excited that he has chosen to join us in Brisbane.”