Academic engagement and the conditions that favor it have become relevant in recent decades due to their relationship with academic performance, well-being, and university permanence. Variables such as perceived social support and sense of belonging are relevant aspects of social integration to promote engagement. Evidence shows both variables predicting engagement. In addition, the available evidence suggests this possible mediating role, which requires further analysis in freshmen in the emergency teaching context due to the COVID-19. The present study aims to evaluate the mediating role of sense of belonging in the relationship between perceived social support and engagement in university students. Results showed significant predictive relationships between social integration variables and engagement and showed the mediating role of sense of belonging in the relation between perceived social support and the three types of engagement. These results suggest the relevance for degree programs to consider these social integration variables as a key element for university freshmen.