Problem-Based Learning (PBL) is a useful learner-centered approach in which learners collaborate within small groups to solve an authentic ill-structured problem that has no right or wrong answer. However, facilitating and designing PBL can be challenging for teachers as well as for learning environment with learners with diverse needs. The main purpose of this action research is to upsurge the academic triumph of Grade 12 Senior High School Learners using PBL in teaching Social Science Classroom. Specifically, this action research sought to answer the following questions: (1) what is the level of learners academic performance in terms of their quarterly grades in UCSP as to their 1st Quarter Grade and 2nd Quarter Grade? (2) what is the mean difference between learners academic performance in terms of their 1st and 2nd quarter grade in UCSP? and (3) how do the learners describe their lived experiences during and after the implementation of problem-based learning as a learner-centered approach in teaching social science classroom? The study is limited to Grade 12 learners from Understanding Culture, Society, and Politics Class of Sta. Catalina Integrated National High School from September 2022 to October 2023. In the conduct of the action research, Mixed Method Research was used to gather necessary data and information. Mean and standard deviation were analyzed using descriptive statistics for quantitative data and thematic analysis for qualitative data gathered from focus group discussions. The findings have shown that PBL as a learner-centered approach to teaching social science, had a large and positive effect to upsurge the academic triumph of Grade 12 learners which marks Very Satisfactory on the level of their academic performance in UCSP Class. For an instance, the conduct of more studies on the different factors affecting PBL integration and specific effects of PBL on various learner domain is recommended to facilitate comparative educational research in the future.