Owner behaviour change may be the most promising avenue to improve dog welfare. As such, understanding potential drivers of owner behaviour is critical to developing effective intervention programs. Here we examine in depth the concept of “duty of care” as a motivator of owner behaviour. Using a mixed methods approach, this study aimed to better understand the potential dimensions of duty of care, their interrelationships, and develop psychometrically valid tools to measure them in companion dog owners. This was achieved through a multi-stage process including a critical literature review, qualitative interviews (n= 13), and an online survey (n= 538). Using Schwartz’s Norm Activation Model as a framework, we have developed a 30 item scale with 5 subscales; duty beliefs, problem awareness, awareness of impact, efficacy, and ascription of responsibility. These unique subscales demonstrate good internal consistency and construct validity. In addition to developing a measurement tool, this process has provided important insights into the nature of duty of care in companion dog owners, creating several avenues for future inquiry. One such finding was that many dog welfare problems may not be the result of lacking duty beliefs, but rather weaknesses in other “activation” factors such as problem awareness or ascription of responsibility. Further work is now required to understand the predictive validity of the scale and the relative influence of its different dimensions on owner behaviour and dog welfare outcomes. This will facilitate the identification of appropriate targets for intervention programs aimed at improving owner behaviour and consequently, dog welfare.