The purpose of this study was to investigate whether self-regulated learning strategies predicted students‟ writing skills/performance, self-efficacy, and critical thinking. The study participants consisted of eleven English majors who were taking the course, Advanced Writing Skills I, in the 2024/2025 academic year. An interrupted time-series within-group design was employed. Repeated measures MANOVA, repeated measures ANOVA, narration, and textual analysis were used to analyze the data obtained from writing tests, self-efficacy questionnaire, diary entries, and essay excerpts, respectively. Accordingly, a multivariate MANOVA results (F(9, 2) = 24.960, p = .039, Wilks’ λ= .009, ηp2= .991) revealed a significant effect of self-regulated learning strategies on writing performance and critical thinking. Likewise, the univariate MANOVA indicated a significant effect of these strategies on writing performance and critical thinking. The tests of within-subjects effects in repeated measures ANOVA (F(1.831, 18.310) = 392.511, p = .000, ηp2 = .975) also showed that the mean scores of the participants for writing self-efficacy changed over the six time points. Moreover, the results of the analysis of the diary entries evidenced that the application of self-regulatory strategies in EFL writing class was effective in enhancing the intended dependent variables. In terms of writing skills, organization, mechanics, grammatical accuracy, and coherence and cohesion were relatively significantly improved. With respect to self-efficacy, most of the students reported improved capability belief in writing. Regarding critical thinking, the participants were able to identify and analyze claims and arguments, interpret and explain controversial issues, evaluate the weakness and strength of their essays, and give judicious conclusions. Regarding their progress across time, slightly improved writing and critical thinking skills were reported during the first diary entry than before while significant progress was reported during the second diary entry better than ever before. Besides, textual analysis of essay excerpts moderately supported the results of diary entries. Overall, the findings were largely positive, with the exception of few qualitative findings, and the participants, indeed, perceived that the instruction in self-regulated learning strategies in EFL writing classes was motivating, encouraging, commendable, and enjoyable. Thus, the combined results indicate the need to incorporate these strategies in the instructional process.