Background: Behavioural interventions for the early prevention of childhood obesity mostly focus on English-speaking populations in high-income countries. Cultural adaptation is an emerging strategy for implementing evidence-based interventions among different populations and regions. This paper describes the initial process of culturally adapting Healthy Beginnings, an evidence-based early childhood obesity prevention program, for Arabic and Chinese speaking migrant mothers and infants in Sydney, Australia. Methods: The cultural adaptation process followed the Stages of Cultural Adaptation theoretical model and is reported using the Framework for Reporting Adaptations and Modifications-Enhanced. We first established the adaptation rationale, then considered program underpinnings and the core components for effectiveness. To inform adaptations, we reviewed the scientific literature and engaged stakeholders. Consultations included focus groups with 24 Arabic and 22 Chinese speaking migrant mothers and interviews with 20 health professionals. With input from project partners, bi-cultural staff and community organisations, findings informed cultural adaptations to the content and delivery features of the Healthy Beginnings program. Results: Program structure and delivery mode were retained to preserve fidelity (i.e. staged nurse calls with key program messages addressing modifiable obesity-related behaviours: infant feeding, active play, sedentary behaviours and sleep). Qualitative analysis of focus group and interview data resulted in descriptive themes concerning cultural practices and beliefs related to infant obesity-related behaviours and perceptions of child weight among Arabic and Chinese speaking mothers. Based on the literature and local study findings, cultural adaptations were made to recruitment approaches, staffing (bi-cultural nurses and project staff) and program content (modified call scripts and culturally adapted written health promotion materials). Conclusions: This cultural adaptation of Healthy Beginnings followed an established process model and resulted in a program with enhanced relevance and accessibility among Arabic and Chinese speaking migrant mothers. This work will inform the future cultural adaptation stages: testing, refining, and trialling the culturally adapted Healthy Beginnings program to assess acceptability, feasibility and effectiveness.