Our cross-sectional finding on the mediating role of purpose in life reveals a psychological mechanism useful for future interventions. Furthermore, the longitudinal influence of pre-pandemic loneliness on purpose in life deserves both scholarly and clinical attention. Most importantly, the longitudinal effects of purpose in life on loneliness and protective behaviors provide guidance for preparing older adults during normal times to cope with loneliness and to comply more with recommended measures during future health crises (such as the COVID-19 pandemic).