Despite the growing interest in unveiling the effect of attributions on L2 learning, there is a dearth of literature on the relationships between attributions and other motivational factors to better explain the motivation of second language (L2) learners. To fill this gap, this study examined the antecedents (language mindsets) and consequences (learning engagement) of students’ attributions to their writing achievement with a sample of 242 second-year students from a Chinese high school. Structural equation modeling results demonstrated the positive associations between growth mindset and internal attributions (i.e., ability and effort) and between fixed mindset and external attributions (i.e., context and luck) to their writing achievement. Further, internal attributions were positively associated with behavioral, emotional, and cognitive engagement, whereas external attributions were negatively related to these three types of learning engagement, with context attribution showing no relationship with behavioral engagement. In terms of the indirect effect, only one path from fixed mindset to emotional engagement via luck attribution was evident. The study contributes to the literature by exploring the nuanced relationships between language mindsets, attributions, and learning engagement in L2 writing learning, based on which pedagogical implications and suggestions for future research are proposed.