The current literature on the behaviour, health, and management of companion dogs (Canis lupus familiaris) indicates that their welfare is often compromised. While there are many factors that have the potential to influence the welfare of companion dogs, carer behaviour is highly influential. Therefore, in order to improve the welfare of companion dogs, it is vital to understand the general and specific human factors that underpin carer behaviour. One such factor that has received little attention in the scientific literature is ‘duty of care’. This paper will firstly review several extant, empirically validated models of human behaviour including the Cognitive Hierarchy model, the Schwartz Theory of Basic Human Values, the Theory of Planned Behaviour, and Hemsworth and Coleman's Animal-Carer model. Secondly, by combining aspects of moral obligation and care, a strong theoretical argument will be presented for the role of ‘duty of care’ as a fundamental motivational driver of animal-carer behaviour. Finally, by integrating ‘duty of care’ with the aforementioned existing models, a hypothesised model of Pet Care Competency is presented, providing a more detailed representation of animal carer motivations than previously documented. Drawing together this wide range of behavioural research and psychological theory, the Pet Care Competency model provides a strong conceptual framework for future empirical investigation. Once the relevant values, beliefs, and attitudes that underpin ‘duty of care’ and contribute most strongly to an individual's Pet Care Competency are identified, this model can be utilised to inform behaviour change programmes that aim to improve carer behaviour and, consequently, dog welfare. By employing this model to identify and target the key elements of carer motivation, a more enduring outcome may be achieved than traditional knowledge-based interventions. This work has the potential to significantly improve the outcomes of animal welfare education and intervention programmes, warranting further exploration.