Group Reading Strategy (GRS), a collaborative reading activity, offers individual contributions to a shared goal using an active learning approach. This mixed-methods research examined the effect of GRS on the critical thinking skills of Thai EFL university learners and explored learners’ perceptions of the GRS process. The critical thinking self-assessment questionnaire, a logbook, and semi-structured interviews were used to collect data. The analysis of the quantitative findings revealed that GRS fostered critical thinking skills in Thai EFL university learners. The results also showed that some intrinsic characteristics of critical thinking skills were cultivated before others. Overall, the current study demonstrated an increase in critical thinking skills through the GRS learning process. The qualitative findings revealed that participants held positive opinions regarding the GRS approach to facilitate active learning environments. Specifically, Thai EFL university participants viewed GRS as peer-assisted learning and a collaborative learning approach, which could, in turn, lessen adverse learning factors. However, some factors, including culture, time-allocation for the GRS process, and types of assessment, also influenced the learning process of GRS activities. Overall, this study indicates that GRS could have an impact on Thai EFL university learners’ critical thinking skills, at least to some extent. However, longitudinal studies are still required in future investigations.