Sense of purpose is seen as a catalyst for successful ageing, predicting a wide range of health outcomes and mortality. However, its role in fostering subjective well-being during old age has received less attention, especially the bidirectional nature of this relationship. The present study examined how sense of purpose predicts and is predicted by subjective well-being in this life stage. Panel data from the Health and Retirement Study ( N = 8980) were used, spanning three measurement occasions across eight years. Four subjective well-being indicators (life satisfaction, depression, positive- and negative affect) were modelled with purpose using (random-intercept) cross-lagged panel models to disentangle within-from between-person associations. We found moderate to strong correlated change and some evidence for directional associations between the constructs. Purpose predicted changes in all four subjective well-being markers, and these associations were generally stronger than the effects of subjective well-being on purpose. Within-person changes in sense of purpose predicted subsequent changes in life satisfaction and positive affect, but not in negative affect and depression. In sum, sense of purpose is associated with higher subjective well-being in old age, but efforts to maintain or increase older adults' sense of purpose may only improve positive components of subjective well-being.