Ritchie joins the Students from SuperSport United, where he played second fiddle to Zimbabwean full-back Onismor Bhasera.
He joins Lehlohonolo Majoro, Edwin Gyimah and Denis Weidlich, who all arrived earlier this year.
Ritchie only featured twice in all competitions for Matsatsantsa during the first half of the campaign.
The 27-year-old will be expected to add some much-needed steel on the left hand side of the Wits defence, where Sifiso Hlanti has been a regular.
Ritchie's PSL career has seen him play for Moroka Swallows, followed by two spells with Kaizer Chiefs, Bloemfontein Celtic and recently Matsatsantsa.