Limited research exists regarding healthcare professionals' knowledge and practice of physical activity promotion for cancer survivors in Ireland. There is also a lack of research identifying the barriers experienced by oncology professionals when promoting physical activity, or referring patients to community-based exercise programmes. This study aims to identify healthcare professionals' knowledge, barriers and practices in relation to physical activity promotion for cancer survivors, and to generate guidance regarding the optimisation of the referral process to community-based exercise programmes. Oncology healthcare professionals (n = 114) were invited to participate in two rounds of an online Delphi study. The response rates in rounds one and two were 38% (43/114) and 70% (30/43). Most respondents acknowledged the value of physical activity for cancer survivors (≥86%) and agreed that discussing physical activity with cancer patients was part of their role (88%). However, the majority of recommendations provided to patients did not align with the current physical activity guidelines. Strategies related to four themes that could optimise the referral process to community-based exercise programmes achieved consensus, including providing education to healthcare professionals and patients regarding the benefits of physical activity and the logistics and quality of programmes, and optimising the logistics of the referral process.