Objective To compare long‐term quality of life outcomes by marital status among women living with breast cancer, and to test the mediation effects of social support as an underlying factor. Methods Data are drawn from 1996 to 2010 of the Australian Longitudinal Study on Women's Health. The sample included 505 women with breast cancer with six years of follow‐up data. Social support was measured by the Medical Outcomes Study Social Support Survey (MOS‐SSS). Physical and mental health‐related quality of life (HRQOL) was measured using the Short‐Form Health Survey (SF‐36). Results Breast cancer survivors who did not have a partner, compared to those who had a partner, had significantly lower levels of social support, which was associated with poorer HRQOL. Social support mediated the relationship between not having a partner and poorer HRQOL. Results were consistent after taken into consideration socio‐demographic characteristics, which included age, highest level of education, country of birth, and area of residence. Conclusions Women recovering from breast cancer who do not have partners have poorer physical and mental HRQOL, than those with partners, with a lack of social support as an underlying inequality. Partners of breast cancer survivors are importance sources in the provision of social support to help them maintain well‐being and quality of life. Copyright © 2016 John Wiley & Sons, Ltd.