Problem-Based Learning (PBL) is a constructivist, student-centered instructional strategy in which students work collaboratively to solve problems and reflect on their learning experiences to advance or gain new knowledge. PBL was originally developed in medical school programs at the McMaster University in Canada in the 1960s. Since then, much research has highlighted the benefits of PBL for developing students’ mathematical knowledge in more flexible and novel ways than traditional teacher-centered teaching approaches. However, there has been a lack of studies examining how PBL can be applied to mathematics teaching and learning, since studies that have investigated the implementation of PBL outside a medical context are sparse in Brunei Darussalam. Therefore, in this study, we attempted to fill this research gap by exploring the implementation process of PBL in a Year 9 mathematics classroom and its possible impact on students’ learning in mathematics in the context of Brunei Darussalam. The participants of the study consisted of 17 Year 9 students (ages 14-15) from a secondary school in Brunei Darussalam The findings from our study showed that the implementation of PBL helped motivate the students to collaboratively work as a group and learn from their peers and therefore, gradually reduced their dependence on the teacher during the course of the intervention. The results from the students’ performances on the pre-test and the post-test also provided evidence to show that the implementation of PBL could have a positive impact on the students’ learning in mathematics. Directions for future mathematical PBL implementation are also discussed and offered.