BACKGROUND: GPs are well placed to enhance shared decision making (SDM) about treatment for patients with advanced cancer. However, to date, little is known about GPs' views about their contribution to SDM. AIM: To explore GPs' perspectives on their role in SDM about palliative cancer treatment and the requirements they report to fulfil this role. DESIGN AND SETTING: Qualitative interview study among Dutch GPs. METHOD: GPs were sampled purposefully and conveniently. In-depth, semi-structured interviews were conducted, recorded, and transcribed verbatim. Transcripts were analysed by thematic analysis. RESULTS: Fifteen GPs took part in this study. Most of them reported practices that potentially support SDM: checking the quality of a decision, complementing SDM, and enabling SDM. Even though most of the GPs believed that decision making about systemic cancer treatment is primarily the oncologist's responsibility, they did recognise their added value in the SDM process because of their gatekeeper position, the additional opportunity they offer patients to discuss treatment decisions, and their knowledge and experience as primary healthcare providers at the end of life. Requirements for them to support the SDM process were described as: good collaboration with oncologists; sufficient information about the disease and its treatment; time to engage in conversations about treatment; a trusting relationship with patients; and patient-centred communication. CONCLUSION: GPs may support SDM by checking the quality of a decision and by complementing and enabling the SDM process to reach high-quality decisions. This conceptualisation of the GP's supporting role in SDM may help us to understand how SDM is carried out through interprofessional collaboration and provide tools for how to adopt a role in the interprofessional SDM process.