Objectives: To investigate physical activity (PA) promotion practices among primary care health professionals in England. To assess whether attitudes, confidence, role perceptions, knowledge of PA guidelines, and PA behaviour were related to PA promotion practices. To examine the barriers to and facilitators of PA promotion practices. Design: A cross-sectional online survey study with open (free text) questions. Setting: National survey and online-administered survey conducted in England. Outcome measures: The outcome variables were attitudes, confidence, role perceptions, PA behaviour, knowledge of the PA guidelines and PA promotion practices. Structural equation modelling evaluated associations between these variables. Participants: A total of 181 primary care healthcare professionals completed an online survey. The majority were general practitioners (GPs) (66.7%), followed by first contact physiotherapists (13.8%), practice nurses (12.2%) and link workers (7.7%). Results: Most (59%) healthcare professionals did not meet recommended levels of PA and could not accurately identify the PA guidelines (53%). Most provided PA advice to patients but fewer than 40% assessed PA, supported behaviour change or made referrals to PA support programmes. More first contact physiotherapists and link workers reported more frequent engagement in collaborative aspects of PA promotion, including assessing PA motivation, supporting behaviour change and providing follow-up. Confidence in promoting PA (beta=0.30, p<0.001) and positive attitudes (beta=0.30, p<0.001) were the only significant predictors of PA promotion practices. Positive associations were observed between confidence, attitudes, PA behaviour and PA promotion practices. Barriers to PA promotion included time constraints and limited and affordable local PA programmes. Facilitators included time and affordable local PA programmes. Conclusions: Most primary care professionals routinely provide PA advice and feel confident doing so. However, with fewer than half able to accurately recall current PA guidelines and routine assessment and behaviour change support rarely reported, the quality and specificity of this advice remain unclear. While time constraints remain a major barrier to PA promotion, particularly among GPs, the addition of first contact physiotherapists and link workers is likely to enhance capacity for promoting PA in busy primary care settings.