The aim of this study was to evaluate whether the presence of anti-hepatitis B (HBV) c antibodies (HBcAb positivity) could influence the control of Human Immunodeficiency Virus (HIV) viremia in patients living with HIV (PLWH) who switch a to two-drug antiretroviral therapy (2DR) containing lamivudine (3TC) (2DR-3TC). A retrospective observational multicenter study was conducted on 166 PLWH switching to the 2DR-3TC-based regimen: 58 HBcAb-positive and 108 HBcAb-negative patients. The HBcAb-positive PLWH group demonstrated a significantly higher percentage of subjects with very low-level viremia at all time points after switching (6th month: <31% vs. 17.6%, p = 0.047; 12th month 34% vs. 27.5%, p = 0.001; 24th month 37% vs. 34.2, p = 0.003 of the HBcAb-positive and HBcAb-negative groups, respectively) and a higher percentage of subjects with detectable HIV RNA greater than 20 copies/mL 12 and 24 months after switching (12 months 32% vs. 11%, p = 0.001; 24 months 37% vs. 13.9%, p = 0.003 of the HBcAb-positive and HBcAb-negative groups, respectively). Logistic regression analysis showed that an increase in age of ten years (OR 2.48 (95% CI 1.58–3.89), p < 0.0001) and the presence of HBcAb positivity (OR 2.7 (5% CI 1.05–6.9), p = 0.038) increased the risk of detectability of HIV RNA by nearly three-fold after switching to 2DR-3TC.