In the context of People Living with HIV (PLWH), poor health literacy (HL) seems to be linked to poorer health outcomes and reduced engagement in care. Additionally, the level of HL can affect HIV knowledge and may impact adherence to antiretroviral therapy (ART). This research explored the connection between ART adherence, HL, and engagement in care in a cohort of 250 PLWH receiving ART in Italy. A questionnaire was given to PLWH at Policlinico Gemelli in Rome to assess their health literacy and adherence to therapy. The Brief Health Literacy Screening (BHLS) and the Newest Vital Sign (NVS) were used to evaluate subjective and objective HL. Adherence levels were self-reported as poor, good, or excellent, and the assessment included the Patient Health Engagement Scale (PHE-S). Notably, the majority of the sample comprised male individuals (67.9%), with 69.2% reporting a 10-years or longer duration between their HIV diagnosis and their initiation of ART. It was found that PLWH with poor adherence had low schooling, had been living with HIV for 1-5years, were HCV co-infected, had a viremia >50copies/mL, poor health status, poor engagement in care, and poor HL (p = <0.001). They exhibited lower mean scores on the subjective HL scale and lower CD4 T-cell counts and nadir CD4 T-cell counts (p < .001). Our study demonstrated a positive correlation between higher HL levels and improved disease management, treatment adherence, and overall physical and mental well-being. Enhanced HL capabilities are paramount in bolstering health management and treatment adherence.