South Africa implemented Universal Test & Treat (UTT) guidelines in September 2016. We examine HIV/ART knowledge among newly diagnosed from a prospective study enrolling newly diagnosed HIV-positive adults, under same-day ART policy, at four primary health clinics in Johannesburg, South Africa. We describe factors associated with high HIV/ART related knowledge score among newly diagnosed patients using Poisson regression. We included 652 HIV positive adults (64.1% female; median age 33 years (IQR: 28–39). Overall, 539 (82.7%) patients were classified as having high HIV/ART knowledge, 14.7% medium knowledge and 2.6% had low knowledge. HIV/ART knowledge was mainly associated to high English literacy (aRR 0.9 Medium vs High, 95% CI: 0.8–0.9; aRR 0.7 for Low vs High: 95% CI: 0.6–0.9). However, patients who did not disclose their intentions for HIV test (aRR 0.9, not disclosed intentions vs having disclosed intentions to test, 95% CI: 0.8–0.9), participants who indicated concerns with ART (aRR 0.9 moderate to high vs low concerns, 95% CI: 0.8–0.9) were less likely to have high knowledge. Our results highlight a correlation between English literacy and good knowledge. There is a need to make information more accessible in a non-English language. Addressing this gap is critical in achieving the WHO targets.