This mixed-methods study aimed to explore factors contributing to therapeutic inertia among people living with obesity in Canada from the perspective of general/family practitioners (GP/FPs). One-on-one interviews and online surveys guided by the Theoretical Domains Framework were conducted. A total of 20 general/family practitioners were interviewed and 200 general/family practitioners were surveyed. Key findings from interviews were used to guide the development of the survey. Spearman's correlation analysis evaluated the association between general/family practitioners theme domain scores and their familiarity with the 2020 Canadian Adult Obesity Clinical Practice Guidelines. The 200 general/family practitioners surveyed provided representation across Canada, with diversity in age, background, and gender. The most prominent domains related to therapeutic inertia that were positively influenced by familiarity with Clinical Practice Guidelines were Beliefs about Capabilities (rs = .27; p < .01), Skills (rs = .23; p < .01), Behavioural Regulation (rs = .24; p < .01) and Emotions (rs = .23; p < .01). Irrespective of their familiarity with Clinical Practice Guidelines, most general/family practitioners reported that environmental and contextual barriers impact obesity management. Particularly, while financial barriers were reported by participants regardless of Clinical Practice Guidelines familiarity, general/family practitioners familiar with Clinical Practice Guidelines more often reported having time to discuss obesity management with patients. This study identified perceptions, resource and training considerations that contribute to healthcare decision-making and therapeutic inertia in obesity management among general/family practitioners and highlighted key areas to target with interventions in primary care to facilitate obesity management, which should be multi-faceted, with a focus on incorporating obesity education into healthcare providers training programs and improving systemic and financial support.