The defender, 28, joins the club after winning the 2021 COSAFA Cup with the senior South Africa national team this past month.
Dube spent just one season with the GladAfrica Championship outfit and enjoyed a standout campaign after joining from TS Galaxy.
"We would like to confirm the signing of Thabani Austin Dube. The central defender joins Amakhosi from Richards Bay United on a 3-year contract with a further 2-year option," the club statement read.
The left-footed defender will look to compete with Eric Mathoho, Daniel Cardoso, Njabulo Ngcobo, Siyabonga Ngezana and Rama Mphahlele for a spot in the Amakhosi defence.
Sifiso Hlanti - defender (31)
Brandon Peterson - goalkeeper (26)
Phathutshedzo Nange - midfielder (29)
Njabulo Ngcobo - defender (26)
Sibusiso Mabiliso - defender (22)
Kgaogelo Sekgota - winger (24)
Given Thibedi - midfielder (23)
Keagan Dolly (28) - midfielder
Cole Alexander (32) - midfielder