Interpersonal relations refer to an intelligence and competence that enable the establishment and maintenance of mutually satisfying relationships with a variety of people across diverse situations. Academic achievement refers to satisfactory learner performance as shown by grades attained in course-work, tests, continuous assessment and end-of-semester examinations. The study interrogated the relationship between interpersonal relations (IR) and academic achievement (AA) among university upgrading (Grade V) teacher students in Ugandan universities. Using a quantitative sample of 473 and a qualitative sample of 75 upgrading Grade V teacher-students from Makerere University and Uganda Christian University (UCU), a cross-sectional survey and interview were carried out. The results showed that IR was positively and significantly related to subjective AA (r = 0.23, p < 0.001). However, it was not significantly related to objective AA -- CGPA (r = 0.04, p > 0.05) thus, supporting the hypothesis: There is a positive relationship between IR and AA among university upgrading teacher-students. Qualitative findings showed that team spirit, group work and collegial relations were important aspects of IR. In conclusion, the study stressed collaborative approaches to IR as useful in the 21st century. As a contribution to policy and practice, the study recommends that: for better AA, teacher-students need to have a holistic curriculum to train on IR. Knowledge of negative and positive perceptions of IR are critical for the furtherance of both individual and collaborative functions in teaching, learning, training, and research.