Background Healthcare professionals' (Oncologists, doctors, and nurses) physical activity (PA) recommendations impact patients living with cancer PA levels. General practitioners (GPs) monitor the overall health of patients living with cancer throughout their treatment journey. This is the first study to explore GP's knowledge, attitudes and practices of PA for patients living with cancer. Methods GPs who see patients living with cancer regularly (n = 111) completed a survey based on The Theory of Planned Behaviour (TPB). Participants (GP's) reported knowledge, attitudes, perceived behaviour control and subjective norms of PA within the cancer population. GP recommendation and referral rates of PA were reported. Principal component analysis was conducted to establish a set of survey items aligned to TPB constructs (attitude, subjective norms, perceived control), and multiple regression analyses characterised associations between these predictor variables and (a) recommendation; and (b) referral-of PA to cancer patients. Results GPs (n = 111) recommended PA to 41-60% of their patients and referred 1-20% to PA programs. Multiple regression models significantly predicted the percent of patients recommended PA, p < .0005 adj. R2 = 0.40 and referred PA, p < .0005, adj. R2 = 0.21. GP attitudes and perceived behavioural control and GP's own activity levels were significant predictors of whether patients were recommended and referred for PA, p<0.05. Conclusion GPs reported positive attitudes and perceptions towards promoting PA for their patients living with cancer. Despite having a positive correlation between PA recommendations and referral rates, a gap was evident between GP's PA beliefs and their individual referral practices. More GP's willing to promote and refer their patients for PA, would improve the physical and mental health outcomes of the cancer population.