Problem-based learning approach’s popularity has grown tremendously in Academic Writing courses throughout the world. The rationale for this rise is that students are driven to pinpoint problematic situations, brainstorm, and find a lasting solution collaboratively, thereby sharpening 21st-century skills, such as writing literacy, problem solving, and critical thinking. Although a growing number of studies are prevalent on this promising approach globally, a gap in the literature has been noticed about its influence on increasing university students’ writing competence in Iraq. To this aim, this mixed method research design study was conducted on 50 freshman students at a private university in the even semester of the 2023–2024 academic year via cluster sampling method spanning 12 weeks. Control group students carried out their writing education as in the curriculum; however, experimental group students’ writing lessons were enriched with the principles of problem-based learning. Having analyzed the data by SPSS 29 and MAXQDA, fetched by writing exams and surveys, findings revealed that experimental group students outperformed control group students regarding enhanced writing performance, boosted motivation, and improved critical thinking with statistically proven data by adopting the distinguishing qualities of problem-based learning at the tertiary level in Iraq context. In other words, the post-test writing exam culminated in a 0.003 statistically significant p-value based on the t-test. Complementary surveys also unearthed a positive correlation between employing problem-based writing instruction and increasing motivation as well as critical thinking skills. The findings of this study may have certain implications for stakeholders who have sought ways to integrate problem-based learning into tasks in Academic Writing courses through a well-established plan and meticulously monitored writing process on a global scale.