Although the negative consequences of workaholism for well‐being are well‐known, research on its underlying processes and potential boundary conditions is scarce. Drawing on the conservation of resources theory, we propose that self‐care mediates the negative association between workaholism and well‐being, such that workaholism decreases self‐care, which, in turn, increases well‐being. Building on the social identity approach, we further argue that group identification moderates the workaholism–self‐care‐link, such that the more individuals identify with their groups, the stronger the negative indirect association. We tested our assumptions in a longitudinal three‐wave study among students (Study 1, NT1 = 300, NT2 = 211, NT3 = 164), in which we found that the indirect association between workaholism and well‐being via self‐care was only significant for those students who more highly identified with their group. We replicated this contingency of the workaholism–self‐care association on group identification in a two‐wave time‐lagged study among employees (Study 2, NT1 = 335, NT2 = 134). Taken together, these findings help gain a deeper understanding of why and when workaholism decreases well‐being.