This mixed-design study examined the effect of a process-genre approach on L2 writing self-efficacy and writing performance. Thirty-one English majors, at the Faculty of Education at New Valley University, acted on as one study group. The tools of the study included a writing self-efficacy scale (designed by the researcher), an English writing test (adapted from TOFEL) and follow-up interviews (designed by the researcher). The tools were administered to the study group before and after the intervention. A 12-week writing intervention course was based on a recent process-genre model suggested by Huang and Zhang (2020). The results of the study showed significant improvements in the students' self-efficacy, overall writing performance and the writing analytic traits (content, organization, vocabulary, language use and mechanics) and writing self-efficacy. The qualitative data triangulated the quantitative large effect size of the intervention. The main emerging theme is the process-genre approach as a supportive environment. Students' accounts showed four intertwined factors contributing to the students' positive perceptions of this method; namely, academic writing support, teacher's scaffolding and peers' assistance, emotional gains and technical writing improvement. The findings of this study support the use of the process-genre approach in teaching writing. Some recommendations for further research and pedagogical implications for teaching English writing are presented.