The National Health Insurance (JKN) program, administered by BPJS Kesehatan, represents a strategic policy of the Indonesian government aimed at achieving inclusive and sustainable access to healthcare services. Although enrolment rates continue to rise, the utilization of BPJS Kesehatan services still exhibits significant regional variation. Most prior research has focused on aspects such as participant satisfaction, service quality, and program implementation evaluation, whereas studies specifically examining the public's decision-making process regarding the use of BPJS Kesehatan services remain relatively limited. Furthermore, few studies have integrated socialization as a determinant of healthcare utilization behaviour within the framework of the Theory of Planned Behaviour (TPB). Therefore, this study aims to analyse the influence of BPJS Kesehatan socialization—both direct and indirect—on the public's decision to use BPJS Kesehatan services in Makassar, while interpreting the findings through the TPB perspective, which encompasses attitude, subjective norms, and perceived behavioural control. This study employs a quantitative approach utilizing an explanatory research design and path analysis. The study population consists of Makassar residents registered as active BPJS Kesehatan participants. The sample comprises 100 respondents selected via purposive sampling. Data were collected using a structured questionnaire based on a five-point Likert scale and analysed using descriptive statistics, validity and reliability tests, classical assumption tests, and path analysis. Test results indicate that all research instruments are valid and reliable, with Cronbach’s Alpha values exceeding 0.70, making them suitable for testing the empirical model. The results demonstrate that direct socialization has a positive and significant influence on the public's decision to use BPJS Kesehatan, with a path coefficient of β = 0.521 (p < 0.001), while indirect socialization also exerts a positive and significant influence, with a path coefficient of β = 0.317 (p < 0.001). These findings indicate that face-to-face communication, outreach sessions, consultations with staff, and direct interactions are more effective than information dissemination via mass media or digital channels. The coefficient of determination (R² = 0.612) reveals that both forms of socialization explain 61.2% of the variation in the public's decision to use BPJS Kesehatan. From the perspective of the Theory of Planned Behaviour (TPB), socialization plays a role in shaping positive attitudes toward the benefits of BPJS Kesehatan, reinforcing social norms that support service usage, and enhancing public perceptions regarding ease of access and the ability to utilize available health services. These three aspects simultaneously drive the formation of the decision to use BPJS Kesehatan. This study contributes theoretically by extending the application of TPB to the context of health policy and public services in Indonesia. Practically, the findings yield an empirical model that can serve as a basis for formulating sustainability strategies for the JKN program—specifically through strengthening community-based socialization, improving public health literacy, and developing more participatory public communication. Furthermore, this study developed the BPJS Utilization Decision Scale (BUDS) as an instrument to measure the determinants of public decisions regarding the use of BPJS Kesehatan in a more comprehensive manner.