Teachers differ in the extent to which they support their students' basic psychological needs. To better understand these differences, we investigated how mindsets and motivation to teach English relate to their need-supportive teaching practices. Data was gathered from 348 EFL instructors (261 female, 87 male; M[subscript age] = 38.47, SD = 9.22) working at state and private universities in Turkey through the following self-report questionnaires: the Implicit Theories of Intelligence Scale (ITIS; Dweck et al., 1995), the Comprehensive Relative Autonomy Index (C-RAI; Sheldon et al., 2017), and the Teacher as a Social Context Questionnaire (TASC-Q; Belmont et al., 1988). Results of structural equation modeling revealed that language instructors' fixed teaching mindset beliefs had both direct and indirect relationships with their need-supportive teaching through quality of teaching motivation. The direct relationships suggest that instructors who believe their teaching ability is a fixed trait are less likely to teach for autonomous reasons, such as personal interest and values, and more inclined to teach out of external reasons, such as pressure from supervisors. The indirect relationships suggest that autonomous teaching motivation mediates the negative relationships between fixed teaching mindset and provision of involvement and structure. These findings highlight the important role of teaching mindsets and motivation in promoting need-supportive learning environments.