(1) Background: An individual’s health status can be perceived as a consequence of their health behaviours. This research aimed to determine the intensity of health-promoting behaviours and to identify factors determining the health behaviours of nursing students during the COVID-19 pandemic. (2) Methods: This study included 894 nursing students from six universities in Poland, and it was conducted between 20 March and 15 December 2021. A diagnostic survey was applied as the research method, and the data were collected using the Health Behaviour Inventory and the Satisfaction With Life Scale. (3) Results: Nearly half of the students participating in the study (48.43%) declared that the intensity of their general health behaviours was low. A positive and significant correlation (r = 0.426) was found between general health behaviours and satisfaction with life. A regression model demonstrated general satisfaction with life to be a predictor of taking up health-related behaviours (18%; β = 0.34), as well as in terms of proper eating habits (4%; β = 0.15), prophylactic behaviours (6%; β = 0.21), positive mental attitudes (26%; β = 0.44) and applied pro-health practices (10%; β = 0.25). (4) Conclusions: Most nursing students showed low levels of health-promoting behaviours. More research is needed on health behaviours and their determinants among nursing students, as it may be important in explaining the mechanisms of health behaviour formation.