<p>Pet ownership is widely studied with respect to human well-being but inconsistent findings underscore its unclear psychological mechanisms and effects. Here, we compare the well-being of pet owners and non-pet owners and investigate the roles of loneliness, living arrangement, and pet attachment in explaining the effects of pet ownership. The results indicated that pet owners experienced lower loneliness than non-pet owners when living alone, such that loneliness mediated the effects of pet ownership on well-being. Furthermore, the interpersonal substitution aspect of pet attachment was prominently associated to well-being, with loneliness completely mediating its negative effects. This study contributes to a more contextual and attachment-focused understanding of how pet ownership could implicate loneliness and well-being. It emphasizes the need to foster healthy pet attachments and to balance pet companionship with human social interactions.</p>