BACKGROUND: The rising prevalence of pretreatment drug resistance (PDR) to non-nucleoside reverse-transcriptase inhibitors threatens the effectiveness of ART. In response, the WHO recommends dolutegravir-based ART regimens due to their high genetic barrier to resistance and better treatment outcomes. This is expected to contribute to achieving the Joint United Nations Programme on HIV/AIDS (UNAIDS) target of 95% viral suppression in people on ART. OBJECTIVES: To estimate the prevalence of PDR among adults initiating ART and assess viral suppression and acquired HIV drug resistance (ADR) among individuals receiving ART in Belize. PATIENTS AND METHODS: Nationally representative cross-sectional PDR and ADR surveys were conducted between 2021 and 2022. Sixty-seven adults were included in the PDR survey, and 43 children and adolescents and 331 adults were included in the ADR survey. Demographic and clinic data and blood specimens were collected. HIV drug resistance (HIVDR) was predicted using the Stanford HIVdb tool. RESULTS: The prevalence of PDR to efavirenz or nevirapine in adults was 49.3% (95% CI 42.2%-56.4%) and was significantly higher in those with previous antiretroviral exposure (OR: 7.16; 95% CI 2.71-18.95; P = 0.002). Among children and adolescents receiving ART, 50.0% had viral suppression, with better rates for those receiving dolutegravir-based ART (OR: 5.31; 95% CI 3.02-9.34; P < 0.001). In adults, 79.6% achieved viral suppression. No resistance to integrase inhibitors was observed in those on dolutegravir-based ART. CONCLUSIONS: Prioritizing dolutegravir-based ART is critical for achieving HIV epidemic control in Belize. Efforts should focus on retention in care and adherence support to prevent HIVDR.