Background HIV/AIDS remains the leading cause of morbidity and mortality worldwide. Moreover, sub-Saharan countries, including Ethiopia, are highly affected by HIV/AIDS pandemic. Ethiopia’s government has been working on a comprehensive HIV care and treatment programme, including antiretroviral therapy. However, evaluating client satisfaction with antiretroviral treatment services is not well studied. Objectives This study aimed to assess client satisfaction and associated factors with antiretroviral treatment services provided at public health facilities of Wolaita zone, South Ethiopia. Methods A facility-based cross-sectional study involved 605 randomly selected clients using ART services from six public health facilities in Southern Ethiopia. A multivariate regression model was used to see an association between independent variables and the outcome variable. The odds ratio with 95% CI was computed to determine the presence and strength of the association. Results Four hundred twenty-eight (70.7%) clients were satisfied with an overall antiretroviral treatment service, which included significant variations ranging from 21.1% to 90.0% among health facilities. Sex [AOR = 1.91; 95% CI = 1.10–3.29], employment [AOR = 13.04; 95% CI = 4.34–39.22], clients’ perception of the availability of prescribed laboratory services [AOR = 2.56; 95% CI = 1.42–4.63], availability of prescribed drugs [AOR = 6.26; 95% CI = 3.40–11.52] and cleanliness of toilet in the facility [AOR = 2.83; 95% CI = 1.56–5.14] were factors associated with client satisfaction with antiretroviral treatment services. Conclusion The overall client satisfaction with antiretroviral treatment service was lower than the national target of 85%, with a marked difference among facilities. Sex, occupational status, availability of comprehensive laboratory services, standard drugs, and cleanliness toilets in the facility were factors associated with client satisfaction with antiretroviral treatment services. Sex-sensitive services needed to address and sustained availability of laboratory services and medicine recommended.