After requesting a release from the Warriors at year's end on personal grounds, Barnett is set to link with the reigning premiers on a two-year deal from 2027.
There is also a mutual option for a third year in 2029, if both the Broncos and Barnett wish to continue his stay.
Barnett's deal offers Brisbane a ready-made replacement for Payne Haas, after the star front-rower's shock defection to South Sydney for next season.
It comes after Barnett had declared he wanted to move back to Australia for his son's medical treatment, with family on the NSW mid-north coast in Taree.
Parramatta and Manly had also been in contention for Barnett's signature, with the 31-year-old having spoken to both clubs before opting to prioritise the Broncos.
In order for Barnett to officially be released by the Warriors, the Auckland-based club will want a player in return.
"Everyone is aware of that. We are waiting to understand what that could look like," Warriors CEO Cameron George told AAP.
"I am not going to name names. We are in talks with Brisbane and waiting to hear back from them."
After leaving Newcastle at the end of 2022, Barnett has developed into one of the best front-rowers in the competition.
At the same time, the volume of top-tier props has decreased, making him one of the most valuable commodities on the market for 2027.
George said the Warriors had always put Barnett's welfare at the forefront when agreeing to release him, but they also require playing talent from Brisbane so they are not disadvantaged.
"The most important thing since Mitch and I had the conversation was that it is all about him and his family," George said.
"The decision from then on was for Mitch to make and not for us.
"Equally we are waiting to understand what the transaction looks like but I am extremely happy for Mitch and his family."
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