Teachers’ leadership behavior has been demonstrated to play a critical role in students’ motivation, learning and performance in school. Given its importance, we theorised and tested a model of the determinants for teachers to excel in leadership behavior in the classroom and beyond. Based on self-determination theory, we modelled the influence of teachers’ self-efficacy and social support on their motivation and, in turn, their leadership behavior. Data analysis was conducted in two main phases: (1) preliminary analyses, including descriptive statistics and correlation testing, and (2) structural equation modelling was conducted using IBM SPSS AMOS 26.0. We used survey data from 199 elementary school teachers which showed the dual relevance of self-efficacy as an intrinsic factor and social support as the extrinsic factor for teachers’ motivation and subsequent engagement in leadership behaviour. The findings demonstrate their interactive and mediated influence on motivation and suggest moving beyond single-factor explanations of teacher leadership and to understand how psychological and social factors simultaneous influence motivation in the field of education. The result suggests practical implications for teacher education programs, policy and schools to providing teachers with strong social support for their teaching role and supporting them in developing their own self-efficacy. This becomes important for facilitating and stimulating their motivation, which will, in turn, increase their commitment to leadership behavior and further affect teacher-student relations and students’ success in education.