The 23-year-old joined Gallants from lower division side Leruma United ahead of the start of last season, making 35 appearances for the club, scoring three and providing one assist.
Pirates also confirmed that Daniel Msendami and Abdoulaye Mariko will move to Bahlabane Ba Ntwa on a season-long loan deal as part of the full agreement.
Mabuza previously featured for the Buccaneers reserve team before moving to Leruma and becomes the 11th player to be signed by the club during the current transfer window.
"During his time away from the club, Mabuza made encouraging progress and impressed," read the statement on club website.
"His performances at Gallants convinced the club that he is ready to return and take the next step in his career."
Thando Ngwenya's representative Gibson Mahachi has opened up on the AmaZulu striker's rapid rise, revealing the influence that helped shape the Zimbabwean forward into one of the Premier Soccer League's most exciting goal-scorers.
Kaizer Chiefs winger Asanele Velebayi has set himself ambitious targets for the new season as he looks to make a greater impact at Naturena.
Orlando Pirates head coach Abdeslam Ouaddou has provided an update on Mohau Nkota's injury, revealing when the Bafana Bafana winger could return to action.
Mamelodi Sundowns have officially confirmed the signing of Thabang Matuludi, adding one of the country's most highly rated right-backs to an already star-studded squad.
