This study examines how students' writing performance is impacted by their writing self-efficacy, background knowledge, and critical thinking. This study uses a survey method to adopt a quantitative approach. Here, 400 Malaysian University English Test (MUET) candidates from 26 Penang Malaysian schools comprise the sample. The research used basic random sampling. Four instruments have been used to collect the data: one argumentative writing task and three questionnaires. Using Smart PLS 4.0, causal correlational analysis was necessary to test the hypotheses. Results yielded by Structural Equation Modeling (SEM) indicated that background knowledge does not directly affect writing performance. Furthermore, writing self-efficacy, as well as critical thinking directly affect writing performance. This study's results may be used as a springboard to help teachers better understand background knowledge, writing self-efficacy, and critical thinking, as writing is an integral component of MUET. Therefore, it might provide insight into how teachers can help these Second Language (L2) writers enhance their background knowledge, writing self-efficacy, and critical thinking.