Police officers work under demanding emotional, psychological and physical circumstances while interacting with victims, criminals and colleagues. They are faced daily with emotional demands to express positive emotions and, at the same time, are required to suppress negative emotions. Consequently, this influences the emotional regulation strategies (i.e., deep- or surface-acting) they choose to use, which impacts their professional identity and work engagement. We conducted a study to understand whether professional identity mediates the relationship between emotional labour (demands and strategies) and work engagement in a sample of Portuguese police officers. For this purpose, we used a set of four self-administered questionnaires: Emotional Work Requirements Scale (EWRS), Emotional Labour Scale (ELS), Social Identity Scale (SIS) and Utrecht Work Engagement Scale (UWES). 924 police officers from the Portuguese Public Security Police (PSP) participated voluntarily. Our results show that there is a mediating effect of professional identity on the relationship between surface-acting strategies, positive emotion expression and negative emotion suppression demands, and work engagement. Professional identity fully mediates the relationship between negative emotion suppression demands and work engagement. Nevertheless, there seems to be no mediating effect of professional identity on the relationship between deep-acting strategies and emotional variety and intensity demands, and work engagement. To the best of our knowledge, no other study has analysed the aforementioned variables in Portuguese police forces. Meaning that our study is ground-breaking, with clear implications. Further research is needed on this subject to understand better the relationship among these variables in the police population.