Problem-based learning (PBL) is an approach where group discussions and collaboration are apparent during problem-solving activities. Accordingly, learners’ personality types that affect the way they think, feel, behave, and interact may potentially have a role in PBL classrooms. This study tries to reveal the possible roles personality types play in PBL by investigating the effects of PBL on the argumentative essay writing of both extroverted and introverted students. This study employed a quasi-experimental design by randomly selecting students in academic writing courses for both the experimental and comparison groups and involving them in the intact classes. The findings revealed that the students in the PBL group scored higher than those in the guided writing group. Moreover, the extroverted students in the PBL group achieved higher mean scores than the extroverted students in the comparison group; however, the difference was insignificant. On the contrary, the statistical analysis showed that the introverted students in the experimental group outperformed those in the comparison group. This is to say that the introverted students taught using PBL had better skills in writing argumentative essays compared to those taught using guided writing techniques. This finding implies the need to use suitable teaching strategies that facilitate both extroverts and introverts in developing their writing skills while also sharpening their communicative and social skills.