Hlanti initially joined Wits in 2015/16 in the January transfer window on loan from National First Division side AmaZulu.
After the end of the 2015/16 season when Hlanti's contract with AmaZulu ended, Wits signed him permanently and midway through this season they added two-year option which the club has now exercised.
The 27-year-old, who is in the Bafana Bafana squad that is in Nigeria for the AFCON 2019 qualifiers, put in some colossal performances for Gavin Hunt's side as they won the Absa Premiership title for the first time in 96-year club existence.
The Newcastle-born player started 26 league matches for Wits and formed a strong partnership at the back with club captain Thulani Hlatshwayo and Buhle Mkhwanazi before the latter suffered a terrible injury.
"Bidvest Wits have exercised a two-year deal they inserted to Hlanti's contract at the start of this past season after he left AmaZulu," the player's agent Sizwe Ntshangase tells this website.
"You remember he came to Wits on loan for six months [in 2015/16] with the one year option. Before the six months loan deal ended Wits exercised the one year option on his contract to sign him permanently and we then negotiated for another two years option which is the one that Wits have exercised now.
"So this is the clean two years and has no option which means this contract will end in 2019. But that option may be inserted because but at this moment in time club's CEO Jose Ferreira is abroad and they want to engage with us by adding a new two-year option on this contract but those talks will begin once Ferreira returns."
Hlanti, who has two Bafana caps, will have some strong competition next season at left back after the Clever Boys signed Bogang Thlone on a pre-contract from Free State Stars in the January transfer window and Thlone's deal will come into effect at the start of next month.