We operationalised the triarchic model of psychopathy (boldness, meanness, and disinhibition) in domestic cats using a cat triarchic (CAT-Tri) questionnaire. In study 1 (n = 549), we identified candidate items for CAT-Tri scales using thematically analysed cat owner questionnaire responses. In study 2 (n = 1463), owners completed a questionnaire battery; the preliminary CAT-Tri questionnaire, Feline Five, and Cat-Owner Relationship Subscales. In study 3 (n = 30), associations between feline daily activity and Cat-Tri scales were investigated. A five-factor cat triarchic plus (CAT-Tri+) solution emerged: boldness, disinhibition, meanness, pet-unfriendliness, and human-unfriendliness. Disinhibition and pet-unfriendliness predicted a higher quality cat-owner relationship; meanness and boldness predicted a lower quality relationship. Findings provide insight into the structure of triarchic psychopathy in cats.