The article analyzes the emergence of the psychosocial field in family justice in Chile as a way of managing and addressing vulnerability. This paper is based on a qualitative field work through interviews with psychosocial professionals in the area of family justice and observations to Family Courts in the Metropolitan Region of Santiago, Chile. We carry out a brief socio-historical review of psychosocial issues in public action and of the role played by untrained legal professionals in the family justice spaces created in the aftermath of the reforms at the end of the 20th century. Then we reflect on the tensions of the professional exercise of these actors, particularly in the treatment of complaints of domestic violence. We conclude that the deployment of the psychosocial field in legal spaces is fundamental in the framework of the new demands of public action that require the inclusion of the vulnerability approach, but that this is also highly associated with the fulfillment of the efficiency mandate required at the procedural level by the new family justice system.