Understanding partnership dynamics is a crucial step in the process of HIV serostatus disclosure to partners. This study examines the relational characteristics associated with HIV serostatus disclosure and the role of disclosure on sexual behaviours within steady partnerships among people living with HIV (PLHIV) in Rio de Janeiro, Brazil. Study participants from 6 large public health facilities were surveyed to investigate psychosocial and relational factors associated with sexual health and well-being. Among 489 individuals in steady partnerships, 86% reported HIV serostatus disclosure to steady partners. After adjusting for demographic variables, attitudes towards disclosure, having an HIV-positive partner, living with partner, and longer relationships were significantly associated with reported disclosure using multivariable logistic regression analysis. Living with partner was negatively associated with partner concurrency. However, having an HIV-positive partner, sex under the influence of drugs or alcohol, and experiencing physical aggression by a steady partner were negatively associated with consistent condom use. Interventions supporting PLHIV to safely and voluntarily disclose to partners may be an effective prevention approach between steady partners, however addressing partner violence and substance use are important considerations for future work.