The important role of willingness to communicate (WTC) in facilitating second language (L2) learning and use has been widely endorsed. However, few studies have examined how teacher support in an L2 class may predict students' L2 WTC. Such a relationship may also be mediated by learners' L2 anxiety, a typical predictor of L2 WTC, and moderated by learners' beliefs about the malleability of their language learning ability, a construct known as growth language mindset. Framed from the Control-Value Theory (Pekrun, in Educ Psychol Rev 18(4):315-341, 2006) and the Language-Mindset Meaning System (Lou and Noels, in: Lamb, Csizér, Henry, Ryan (eds) The Palgrave handbook of motivation for language learning, Palgrave Macmillan, 2019a, System 86:102126, 2019b), this study aimed to investigate the relationships between teacher support, L2 anxiety, growth language mindset, and L2 WTC. The data were collected from 551 English-as-a-Foreign-Language (EFL) learners in Iran and analyzed using structural equation modeling (SEM). The results showed that teacher support was directly and positively associated with L2 WTC, and this relationship was significantly mediated by L2 anxiety. The relationship between teacher support and L2 WTC, however, was only significant among learners with medium and high levels of growth language mindset. In addition, growth language mindset also moderated the negative relationship between L2 anxiety and L2 WTC, with this relationship being weaker among learners with higher levels of growth language mindset. Finally, theoretical and pedagogical implications and directions for future research are presented.