Globally, in 2017 35 million people were living with HIV (PLHIV) and 257 million had chronic HBV infection (HBsAg positive). The extent of HIV‐HBsAg co‐infection is unknown. We undertook a systematic review to estimate the global burden of HBsAg co‐infection in PLHIV. We searched MEDLINE, Embase and other databases for published studies (2002‐2018) measuring prevalence of HBsAg among PLHIV. The review was registered with PROSPERO (#CRD42019123388). Populations were categorized by HIV‐exposure category. The global burden of co‐infection was estimated by applying regional co‐infection prevalence estimates to UNAIDS estimates of PLHIV. We conducted a meta‐analysis to estimate the odds of HBsAg among PLHIV compared to HIV‐negative individuals. We identified 506 estimates (475 studies) of HIV‐HBsAg co‐infection prevalence from 80/195 (41.0%) countries. Globally, the prevalence of HIV‐HBsAg co‐infection is 7.6% (IQR 5.6%‐12.1%) in PLHIV, or 2.7 million HIV‐HBsAg co‐infections (IQR 2.0‐4.2). The greatest burden (69% of cases; 1.9 million) is in sub‐Saharan Africa. Globally, there was little difference in prevalence of HIV‐HBsAg co‐infection by population group (approximately 6%‐7%), but it was slightly higher among people who inject drugs (11.8% IQR 6.0%‐16.9%). Odds of HBsAg infection were 1.4 times higher among PLHIV compared to HIV‐negative individuals. There is therefore, a high global burden of HIV‐HBsAg co‐infection, especially in sub‐Saharan Africa. Key prevention strategies include infant HBV vaccination, including a timely birth‐dose. Findings also highlight the importance of targeting PLHIV, especially high‐risk groups for testing, catch‐up HBV vaccination and other preventative interventions. The global scale‐up of antiretroviral therapy (ART) for PLHIV using a tenofovir‐based ART regimen provides an opportunity to simultaneously treat those with HBV co‐infection, and in pregnant women to also reduce mother‐to‐child transmission of HBV alongside HIV.