Willingness to communicate in a foreign and second language (L2 WTC) has gradually become a recurrent theme in the SLA. With the advent of an emotional or affective turn brought by the positive psychology movement in applied linguistics, the significant role of positive emotions such as Foreign Language Enjoyment (FLE) in L2 WTC has been highlighted. Nevertheless, the mechanism underlying the association between FLE and L2 WTC has received little attention. Drawing on Fredrickson's broaden-and-build theory, the present research examined the influence of FLE upon L2 WTC with Growth Language Mindset (GLM) and grit examined as potential mediators through structural equation modelling. To this end, 2426 undergraduate students from 29 universities were asked to fill out an online questionnaire with Likert scale items. The results confirmed that FLE not only directly affected L2 WTC, but exerted an indirect influence on L2 WTC through three paths respectively via the mediating role of GLM, the mediating role of grit and the chain mediating role of GLM and grit. These findings provide empirical evidence from the domain of SLA for the broaden-and-build theory, unveiling the influence mechanism shaping the interconnectedness among all variables. Directions for future research and pedagogical implications are substantially discussed.