Objective This study examined the impact of the COVID-19 pandemic and subsequent social restrictions or quarantines on the mental health of the global adult population. Method A sample of 6,882 individuals (M-age = 42.30; 78.8% female) from 59 countries completed an online survey asking about several pandemic-related changes in life and psychological status. Results Of these participants, 25.4% and 19.5% reported moderate-to-severe depression (DASS-21) and anxiety symptoms (GAD-7), respectively. Demographic characteristics (e.g. higher-income country), COVID-19 exposure (e.g., having had unconfirmed COVID-19 symptoms), government-imposed quarantine level, and COVID-19-based life changes (e.g., having a hard time transitioning to working from home; increase in verbal arguments or conflict with other adult in home) explained 17.9% of the variance in depression and 21.5% in anxiety symptoms. Conclusions In addition to posing a high risk to physical health, the COVID-19 pandemic has robustly affected global mental health, so it is essential to ensure that mental health services reach individuals showing pandemic-related depression and anxiety symptoms.