The aim of this study was to develop, implement and evaluate a physical activity (PA) behaviour change (BC) intervention to increase cancer survivors’ PA levels, cardiorespiratory fitness (CRF) and health-related quality of life (HRQoL). Formative research, consisting of a Delphi study with oncology healthcare professionals(OHPs) and focus groups (FGs) with cancer survivors, was first conducted to inform the intervention design. A two-arm non-randomised comparison trial was conducted to test the intervention. Participants recruited to the trial completed accelerometry, the 6 minute time trial and the Functional Assessment of Cancer Therapy General questionnaire at baseline and months 3 and 6. Participants in the intervention group (IG) received a home-based PA programme, 4 PA information sessions and a one-to-one exercise consultation, in addition to 12 weeks of twice- weekly supervised exercise classes. The control group (CG) received 12 weeks of twice-weekly supervised exercise classes only. The majority of OHPs did not provide. PA recommendations to patients that align with the current PA guidelines. Seven FGs with 41 cancer survivors were conducted. Participants highlighted the need for a holistic approach to rehabilitation. One-hundred and ninety-one cancer survivors participated in the trial (CG, n= 87; IG, n=104; mean age (± SD) 56 ± 10y, 73% female). The trial completion rate was 51%. PA levels, CRF and HRQoL increased for both groups from baseline to 3 months. Improvements achieved at 3 months in CRF were maintained by both groups at 6 months. In addition, increases in light-intensity PA (LIPA), daily steps and HRQoL observed at 3 months, were maintained for IG at 6 month follow-up. Participation in a 12-week exercise programme has a positive long-term effect on cancer survivors’ CRF. The inclusion of additional BC strategies augmented the benefits achieved by also maintaining improvements in daily steps, LIPA and HRQoL at 6 months.