Women with breast cancer make up a significant proportion of cancer survivors, with more than 43,750 women living with breast cancer in Ireland. However, many women report physical and psychological health difficulties that interfere with their ability to return to work. In Ireland, and internationally, these difficulties are being increasingly recognised, with recent research identifying gaps in rehabilitation services to prepare women with breast cancer to return to work. Collaborating with women with breast cancer, and those who provide health and supportive services to individuals living with cancer in Ireland, an online self-management intervention, CanWork, was developed. CanWork aims to support women with breast cancer to manage the process of returning to work and learn strategies to manage post-treatment health-related difficulties. CanWork also provides information on workplace entitlements. This intervention was trialled with women with breast cancer in 2021, who reported that the programme gave them confidence to return to work and that the content was relevant. This study will include a larger group of women with breast cancer to determine if CanWork is effective in supporting return to work. To do this, 248 women with breast cancer will be included in the study, half of whom will receive CanWork and the results will be compared with women who do not receive the intervention. Having a programme that is financially viable is important and therefore the costs involved in running and attending the intervention will also be calculated. Should this study demonstrate that CanWork is effective in supporting women with breast cancer to return to work, the study team will collaborate with cancer services in Ireland to make the programme available nationally.