<p>Empirical evidence from the agricultural sector highlights the importance of psycho-behavioral factors in farmers’ adoption of programs, policies, and technologies, including partnerships. However, psycho-behavioral studies on partnerships remain limited, particularly concerning the factors that motivate farmers to engage in partnerships. Among the first to apply the extended Theory of Planned Behavior (TPB) in the context of partnership adoption, this study investigates the psycho-behavioral drivers of coffee farmers’ intentions to join partnerships. This study explores new dimensions of the TPB framework by integrating Perceived Economic Benefit (PEB) and Past Behavior (PB) with the TPB construct. A face-to-face survey of 300 farmers in July-August 2023 in the Semende Highlands, South Sumatra, was conducted using convenience sampling, with data analyzed using descriptive statistics and Partial Least Squares-Structural Equation Modeling (PLS-SEM). Findings show that PEB is the strongest predictor of intention, followed by Attitude Toward Behavior (ATB) and PB, while Subjective Norm (SN) and Perceived Behavioral Control (PBC) had no significant direct effects. These findings confirm that individual beliefs, economic considerations, and previous experiences are more important than social pressure or perceived ease of participation in shaping the intention to join the partnership. This study also reveals significant relationships between constructs, such as the influence of SN on ATB and PBC, ATB on PBC, PB on PBC, and PEB on ATB, highlighting the theoretical value of incorporating context-specific predictors into TPB. By demonstrating the limitations of the classic TPB in the context of traditional agriculture, this study provides new insights into farmer partnership behavior and offers guidance for policymakers and relevant stakeholders to increase farmer participation in partnerships through economic incentives, evidence-based extension, and experience-sharing strategies.</p>