We tested if challenges to basic psychological needs (BPN) for autonomy, competence, and relatedness during the COVID-19 pandemic undermine people’s mental well-being. Furthermore, we tested if an intervention, affirmation of these psychological needs, enhances mental well-being. Results of Study 1 (N = 153) showed that higher levels of satisfaction of BPN were related to higher well-being during the COVID-19 outbreak. In Study 2 (N = 215), we employed an online intervention enhancing these BPN. We found increased mental well-being through bolstered relatedness in particular. The intervention also decreased perceived stress. Both studies showed that mental well-being during the COVID-19 pandemic is positively related to the ability to work as usual and the number of people contacted via phone or internet but not in person.