Therapeutic radiographers (TRs) are well-placed to deliver advice to cancer patients; however, limited research exists on their practices in providing advice on healthy lifestyle behaviours. Through an online survey, this study aimed to explore TRs’ current practices, barriers, and facilitators around delivering healthy behaviour advice to cancer patients. An online survey was sent to 72 radiotherapy departments in the UK and 583 TRs responded to the survey. Findings showed that levels of enquiry and provision of advice on healthy behaviours were low, with less than 25% advising patients on physical activity, healthy eating, weight management, smoking cessation, and reducing alcohol intake as standard practice. Lack of knowledge, resources, and training were identified as barriers, in addition to perceived lack of patient interest and lack of time. TRs reported a strong desire to undergo training to enable them to deliver health behaviour advice to patients, with an identified preference for online training. Cancer patients look to healthcare professionals for advice on health behaviours, and TRs are well-placed to deliver this advice. The findings of this study provide insight into the areas that need addressing to enable TRs to support positive health behaviours among cancer patients.