Sea Robbers head coach Milutin Sredejovic is confident the 19-year-old - who can play in defence and midfield - is ready for the challenge.
"Mbulu has left a really good impression,” Sredejovic told the club's website.
“I have been monitoring him over the past few months at SAB level. He has also been training with us for a couple of weeks, where has shown that he is ready to take the next step.”
The left-footed Mbulu was a regular member of Pirates' MultiChoice Diski Challenge side and SAB team, while he also went on the 'Project-X' tour to England in 2017.
He hails from KwaZulu-Natal and is the second player to be elevated from Bucs' development structures this season after striker Lyle Foster.