Antimicrobial resistance (AMR) is a major One Health challenge that threatens both human and animal health. While research has largely focused on food-producing animals, antimicrobial use (AMU) in companion animals remains underexplored, despite the close contact between pets and their owners. Understanding the behavioural factors influencing AMU is essential for effective stewardship.  This study explored AMU in dogs and the behavioural factors influencing prescribing by veterinarians and treatment decisions by dog owners in Northern Ireland, applying a behavioural economics approach. Questionnaire data from 355 dog owners were analysed to identify prescribing patterns and behavioural predictors of AMU.  Overall, 58% of dogs had been treated with antimicrobials at least once during their lifetime (mean duration = 6 days, SD = 2.06). The most common antimicrobials were amoxicillin-clavulanic acid and metronidazole, prescribed mainly for skin/wound (25%) and gastrointestinal (18%) infections. Logistic regression identified several significant predictors: older dogs (≥8 years; β = 0.11, p = 0.002), having pet insurance (β = 0.61, p = 0.011), and impatience in the form of present bias (β = 0.52, p = 0.048) were all associated with higher odds of AMU. No significant associations were found for owner’s age, income, education, location, breed, neuter status, or household composition.  Although AMR awareness was limited with only 26% of owners being very familiar with the concept. 87% of owners valued veterinary advice.  These findings highlight behavioural drivers of AMU and the critical role veterinarians may play in promoting stewardship through behaviourally informed communication with dog owners.