Postpartum weight retention contributes to maternal obesity and varies by ethnicity. Despite the well-established benefits of lifestyle intervention on weight management, little is known about how to engage postpartum women effectively, especially among ethnic minority groups. This multi-methods study aimed to explore ethnic differences in women’s preferences for lifestyle intervention after childbirth. Women within five years of childbirth and living with their youngest child in Australia were recruited in an online survey (n = 504) and semi-structured interviews (n = 17). The survey and interview questions were structured based on the Template for Intervention Description and Replication (TIDieR) framework. Ethnic groups were categorized as Oceanian, Asian and Other according to the Australian Bureau of Statistics. Chi-square tests were used to compare the preferred intervention characteristics between groups. Qualitative data were thematically analysed. The survey showed that most women across all ethnic groups were interested in receiving lifestyle support in the early postpartum period (from 7 weeks to 3 months postpartum). All ethnic groups preferred a regular lifestyle intervention delivered by health professionals that promotes accountability and provides practical strategies. However, Asian women had a higher desire for infant care and a lower desire for mental health in the intervention content compared with Oceanian women. Moreover, Asian women were more likely to favour interventions that are initiated in a later postpartum period, over a shorter duration, and with less intervention frequency, compared with Oceanian women. The interviews further indicated the need for intervention adaptations in the Asian group to address the cultural relevance of food and postpartum practices. These ethnic-specific preferences should be considered in the development of culturally appropriate intervention strategies to optimize engagement in healthy lifestyles among the targeted ethnic groups.