The clinical management of people with multidrug-resistant (MDR) human immunodeficiency virus (HIV) remains challenging despite continued development of antiretroviral agents. A 58-year-old male individual with MDR HIV and Kaposi sarcoma (KS) was treated with a new antiretroviral regimen consisting of anti-CD4 domain 1 antibody UB-421 and capsid inhibitor lenacapavir. The individual experienced delayed but sustained suppression of plasma viremia and a substantial increase in the CD4(+) T cell count. A longitudinal examination of plasma HIV and infectious isolates showed no evidence of viral evolution or the emergence of UB-421- or lenacapavir-resistant viruses. The individual received three cycles of liposomal doxorubicin and five doses of anti-programmed cell death protein 1 (PD-1) monoclonal antibody pembrolizumab that resulted in improvement in KS with flattening of lesions. Our data demonstrate that combination therapy with UB-421 could provide sustained virologic suppression in people harboring MDR HIV with limited therapeutic alternatives.