OBJECTIVE: To investigate whether longitudinal changes in health-related quality of life (HRQoL) among breast cancer patients vary by prediagnosis occupational status or postdiagnosis changes in working time. METHODS: We identified 1573 patients in the Breast Cancer Quality Register of Central Sweden and asked them to participate in a longitudinal questionnaire study. A total of n = 841 women completed three questionnaires within a mean time of 4, 16, and 38 months postdiagnosis. Generalized estimating equation models were used to examine changes in European Organization for Research and Treatment of Cancer Quality of Life Questionnaire and the Breast Cancer-Specific Quality of Life Questionnaire subscales stratified by prediagnosis occupational status and postdiagnosis changes in working time. RESULTS: Over time, the proportion of employed women reporting good functioning increased more, and the proportion reporting a high level of symptoms decreased more compared with women on sick leave/disability pension and retirement pensioners (p < 0.001). The latter two also showed a worsening in several subscales (p < 0.05). Among employed women, more consistent improvements in role and social functioning were observed among those with an increase/no change in working time than among those who had decreased it or stopped working (p < 0.05). A decrease in the proportion reporting pain was observed among women with an increase/no change in working time compared with women with decreased working time, among whom the proportion reporting pain increased (p = 0.008). CONCLUSIONS: Being employed prediagnosis and resuming work to the same extent as prior to the breast cancer diagnosis are associated with consistent improvements in HRQoL. These results highlight the importance of interventions to improve HRQoL and policies to support return to work following diagnosis.