The acquisition of L2 writing skills has been deemed a daunting task for most students in ESL and EFL contexts. Therefore, to become effective learners, for example, proficient L2 writers, they need to be guided and taught how to monitor, control, and regulate the learning process involving the aspects of cognition, motivation, behavior, and environments. In other words, they need to acquire self-regulated learning (SRL) skills. Several crucial SRL variables that affect self-regulation of the writing processes need to be further explored in order to have a deeper understanding of students’ self-regulated behaviors in writing tasks. Hence, the purpose of this research was to examine, by testing a theoretical model, the multidimensional nature of the relationship between EFL students’ multiple SRL variables and their writing competence. The subjects of this research comprised 357 Taiwanese undergraduate students from four universities in North Taiwan. Quantitative data gleaned through three questionnaires was analyzed; a paragraph writing test was also administered to assess the participants’ current writing competence. The results of the study are as follows: (1) All factor structures were verified and the proposed structural equation model was also specified, respectively with appropriate reliability and validity; (2) The participants developed more ideal L2 selves instead of ought-to L2 selves; (3) Only ideal L2 selves significantly affected students’ motivation; (4) Ideal L2 selves proved to be a much stronger predictor of extrinsic motivation rather than intrinsic motivation; (5) Both intrinsic and extrinsic motivation positively predicted learners’ proactive actions to teacher written corrective feedback (LPATF); and (6) Both intrinsic and extrinsic motivation had no direct effect on the participants’ writing competence, but LPATF did. The findings of this research reveal implications for L2 writing teachers and program designers on the development of students’ self-regulated learning skills.