This study aims to develop a research and development (R&D) strategy model based on the open innovation approach in the Iranian banking industry. The research adopts a qualitative design grounded in a multi-grounded methodology, which systematically integrates field data with the theoretical foundations of domestic and international studies. Specifically, the study employs the systematic grounded theory approach of Strauss and Corbin within the multi-grounded framework. This alignment with the three-stage coding process (open, axial, and selective coding) and the use of the paradigmatic model, as elaborated in the methodology and findings sections, enhances the methodological transparency of the study. Data were collected through in-depth semi-structured interviews with fifteen banking and academic experts. The sampling process followed a theoretical approach and continued until combined saturation was achieved. Data analysis was conducted through open, axial, and selective coding. The findings indicate that digital transformation, regulatory requirements imposed by the Central Bank, and macroeconomic policies are among the most significant causal factors driving the emergence of open innovation in banks. In response to these drivers, strategies such as multi-institutional collaboration (bank–university–fintech), data infrastructure development, and human resource empowerment emerged as key operational pillars. From a conceptual perspective and based on expert perceptions, the results of the final model suggest that open innovation can contribute to enhanced organizational sustainability, competitiveness, improved quality of digital services, and increased banking brand value. Nevertheless, technological, cultural, and regulatory challenges remain the main barriers to the full realization of this model. Overall, the final model provides a systematic representation of the linkage between environmental drivers, organizational strategies, and the broader outcomes of open innovation. From the perspective of scientific novelty and knowledge contribution, this study offers a localized and integrative model of an open innovation–based R&D strategy tailored to the Iranian banking industry by employing a multi-grounded approach. By explicating the causal relationships among environmental drivers, organizational strategies, and innovation outcomes, the study contributes to the advancement of knowledge in the field of banking innovation and R&D strategy.