Service-learning (SL) is a pedagogical model focused on achieving curricular goals while providing a community service. Previous research suggests that SL might promote qualities such as self-esteem, motivation, problem-focused coping, decision-making, empathy, and communication, which are associated with a psychological construct known as students’ Effective Personality (EP). These studies, however, did not specifically analyse the direct effects of SL on this construct. The aim of this study is to explicitly analyse the effect of SL on Physical Education Teacher Education (PETE) students’ EP using a mixed methods approach. The quantitative part of the approach followed a quasi-experimental design using the validated “Effective Personality Questionnaire for University Students”, which includes four dimensions: “Academic self-efficacy”, “Social self-realisation”, “Self-esteem”, and “Resolutive self-efficacy”. A non-probabilistic sampling on a total of 181 PETE students was then carried out, with 98 participating in the experimental group (42 male, 56 female), and 83 in the control group (34 male, 49 female). The comparisons revealed significant improvements in the experimental group, especially in the social self-realisation and resolutive self-efficacy dimensions. These findings were complemented by a qualitative analysis of 12 students’ semi-structured interviews. In conclusion, the study reported a positive influence of SL on the PETE students’ EP, providing valuable design patterns for future SL implementations.