Addressing the gap in the literature that treats second language (L2) writing competence and emotional well-being as separate domains, this mixed-methods study investigates the impact of strategy-based writing instruction (SBWI) on the writing competence and emotional well-being of Chinese English as a foreign language (EFL) learners. Conducted over a semester at a Chinese state university with 106 sophomore English majors, the experimental group (N = 55, M = 18.96, SD = .637) received strategy-based writing instruction, contrasting with a control group (N = 51, M = 18.90, SD = .664) that received a conventional approach. It assessed writing performance and emotional well-being (operationalized via writing anxiety) across pre-, post-, and delayed post-tests, supplemented by diaries and interviews. Results showed that SBWI significantly enhanced writing cohesion and promoted emotional well-being by reducing cognitive anxiety, compared with conventional methods—qualitative data furthered understanding of the research findings. The study bridges the divide between strategic and affective aspects of writing to improve pedagogical approaches and support students’ writing skills and emotional well-being.