The important role of individual differences in affecting teachers' involvement in and professional development through research has received little systematic attention in theoretical discussions and empirical studies on teacher research. Therefore, relying on the available literature and our proposed theoretical models, we investigated the possible links among language teachers' Big Five personality traits, motivation to conduct research (through self-determination theory's intrinsic and extrinsic motivations alongside the avoidance motivation construct), and teacher research involvement (TRI). Using a survey method, data were gathered from 253 Iranian school English teachers (SETs) and subjected to correlational and structural equation modeling (SEM) analyses. Notably, SEM results demonstrated that Openness to Experience, Conscientiousness, Agreeableness, and Neuroticism significantly predicted the motivational constructs which themselves predicted TRI. Moreover, the effects of these four traits on TRI were fully mediated through the motivational constructs. Implications for theory, policymaking, and professional development in the teacher research field are proposed.