Social unrest, coupled with the outbreak of COVID-19, was a double-hit for Hong Kong in early 2020. Those stressful societal situations not only trigger negative emotions, such as anxiety and/or depression, but also consolidate a person’s belief towards oneself (i.e., meaning in life) and society (i.e., social axioms). The study included 2031 participants from the Formation and Transformation of Beliefs in Chinese (FTBC) project dataset. The data were collected in Hong Kong from February 2020 to March 2020 (double-hit). Path analysis and multiple regression were used to examine the mediating and moderating effects of the presence subscale (P) of the Meaning in Life Questionnaire (MLQ) on the relations between social axioms and negative emotions. Results showed that low MLQ-P mediated the associations between cynicism and negative emotions and between low religiosity and negative emotions and moderated the relation between social cynicism and emotional outcomes. Exploratory analyses showed that MLQ-Search (S) mediated the relations between reward for application and negative emotions, between social complexity and negative emotions, and between fate control and negative emotions, and moderated the relation between religiosity and stress. As far as we know, this study reported the first evidence of the role of meaning in life in explaining and modifying the associations between social axioms and mood states. The presence of and search for meaning in life seem to work differently with respect to the relations between social axioms and negative emotions, with important implications for understanding the dynamics of social and personal beliefs in affecting mental health in times of large-scale public crisis.