Mabiliso, who helped Amajita win the COSAFA U-20 Championships in Zambia on Saturday, has penned a three-year deal with Usuthu.
He will compete with the likes of left-back Simphiwe Mtshweni for game-time at the Premiership outfit.
Club spokesman Brilliant Makhathini confirmed the capture of the Platinum Stars development product.
“Yes, he has signed with us,” Makhathini tells KickOff.com.
“He is a left-back and I believe he was part of Platinum Stars' youth development.”