Aim: The aim of the present study was to describe the development of Families First, a new mentalization-based group intervention model for supporting early parenthood. The general aim of the intervention was to support well-functioning models of parenting and prevent transmission of negative parenting models over generations, and thus promote child development and overall family health. Background: In the Finnish society, great concern has aroused during the last decade regarding the well-being and mental health of children and adolescents. Increased number of divorces, poverty, substance abuse, and mental health problems among parents enhance the risk for child neglect and abuse. New effective, preventive, and health-promoting intervention tools are greatly needed to support families with young children. At present, the Families First intervention is being implemented in primary social and healthcare units all over Finland. Methods and findings: This article will provide a theoretical understanding of the importance of parental mentalization for the development of the parent-child relationship and the development of the child as well as proposed mechanisms of actions in order to enhance mentalizing capacity. The cultural context will be described. The article will also provide a description of the scientific evaluation protocol of the intervention model. Finally, possible limitations and challenges of the intervention model are discussed.