Obesity is a global issue, with healthcare practitioners increasingly involved in clinical interactions with people who are overweight or obese. These interactions are opportunities to provide evidence-based healthy lifestyle advice, and impact on public health. This study used a cross-sectional survey of Australian healthcare practitioners to investigate what influenced the provision of healthy lifestyle advice to obese and overweight clients. A modified theory of planned behavior was used to explore knowledge translation processes. Knowledge translation was linked to three factors: (i) a healthcare practitioner's education and confidence in the currency of their knowledge; (ii) personal characteristics – whether they accepted that providing this advice was within their domain of practice; and (iii) the existence of organizational support structures, such as access to education, and best practice guidelines. To fulfill the potential role healthcare practitioners can play in the provision of evidence-based health promotion advice requires organizations to provide access to practice guidelines and to instill a belief in their workforce that this is a shared professional domain.