A range of factors has contributed to the lack of a clear employment pathway for agricultural students after graduation, underscoring the importance of developing career adaptability. Given a theoretical gap in the existing literature, understanding the mechanisms through which agricultural students develop career adaptability is essential. Accordingly, this study aimed to examine the role of perceived social support and positive self-esteem in the development of career adaptability. Using a quantitative survey design, data were collected from 381 final-year undergraduate students at public universities in Iran through a multi-stage sampling method. The data were analyzed using Partial Least Squares Structural Equation Modeling (PLS-SEM). The results revealed that perceived social support has a significant direct effect on agricultural students’ career adaptability as well as an indirect effect through positive self-esteem, indicating partial mediation. Furthermore, a positive nonlinear (quadratic) relationship was found between perceived social support and career adaptability, suggesting that increases in social support enhance career adaptability at an increasing rate up to a certain threshold. To foster career adaptability among agricultural students, higher education institutions should not only encourage faculty members to provide emotional and informational support but also implement strategies aimed at strengthening students’ self-esteem. Overall, the findings contribute to a deeper understanding of the mechanisms underlying career adaptability and offer practical implications for improving adaptability within agricultural higher education institutions.