The palm oil industry, integral to Indonesia’s economy and the United Nations Sustainable Development Goals (SDGs), faces emerging economic, environmental, and social challenges. These compel the adoption of sustainable agricultural practices, particularly in light of the Indonesian Sustainable Palm Oil (ISPO) certification system’s implementation by 2025. This study develops a model integrating Ajzen’s Theory of Planned Behavior and Rogers’ Diffusion of Innovation theory to elucidate factors influencing farmers’ adoption of sustainable palm oil farming. Data from 300 palm oil farmers in West Kalimantan, Indonesia, were analyzed using structural equation modeling. The results indicated significant positive effects in terms of attitudes, subjective norms, perceived behavioral control, relative advantage, compatibility, and trialability on sustainable practice adoption, while the complexity negatively influenced adoption. These findings underscore the need to address farmers’ motivations, social norms, perceived control, and practice advantages for successful implementation. The study offers critical insights for policymakers and practitioners to formulate strategies that encourage the voluntary adoption of sustainable practices, balancing farmers’ needs and environmental sustainability.