Background <p>The benefits of physical activity are widely recognized in primary and tertiary breast cancer prevention. Most women do not meet the international physical activity recommendations for breast cancer prevention despite public health policies. The aim of this study is to better understand barriers, facilitators, and preferences for physical activity among adult women in France.</p> Methods <p>A web-based observational study was conducted between February and March 2021 through a Seintinelles French collaborative research platform. Women with and without a history of breast cancer were asked to complete an online questionnaire measuring sociodemographic and health characteristics, physical activity behaviors, physical activity barriers and facilitators, and physical activity preferences.</p> Results <p>A total of 2,306 women participated in this study, including women without breast cancer (<i>n</i> = 1,245), women with localized breast cancer undergoing treatment (<i>n</i> = 530), or post-treatment (<i>n</i> = 396), and women with metastatic breast cancer (<i>n</i> = 135). The mean age was 48.7&#xa0;years (SD = 13.2) and 63.8% of the population were classified as insufficiently active. Lack of motivation was the most common physical activity barrier in all groups while the main physical activity facilitators were women's desire to improve their abilities and quality of life, to feel better about their bodies and to experience pleasure. Walking remains the preferred physical activity for all women in the study, as they particularly like to be active outdoors, under supervision, on any day of the week, at a moderate intensity, for 30–60&#xa0;min per session. Some differences of physical activity barriers, facilitators and preferences were observed between women who are still undergoing treatment compared to women who have completed the treatment or without breast cancer history. Women with metastatic breast cancer emphasized their need for physical activity counselling. Overall, physically inactive women reported more barriers to exercise (17 out of 22 items), whereas physically active women reported more facilitators (20 out of 22 items).</p> Conclusions <p>Women across the breast cancer spectrum identified similar and unique determinants and preferences for physical activity. These determinants and preferences may contribute to targeted activity guideline development to promote physical activity for women before, during, and after treatment for breast cancer.</p> Implications for Cancer Survivors <p>Women who had completed treatment for localized breast cancer share both common and specific determinants and preferences for&#xa0;physical activity compared with women without breast cancer, those undergoing treatment, and those with metastatic disease,&#xa0;highlighting the need for tailored physical activity counselling and programs.</p>