Postpartum weight retention (PPWR) is a strong predictor of obesity and associated consequences in later life in women. Suboptimal lifestyle behaviours (e.g. diet and physical activity) contribute to PPWR. Postpartum lifestyle interventions are known to be efficacious in reducing PPWR, however, there are challenges to their successful implementation. According to the Consolidated Framework for Implementation Research, identification of core intervention components across intervention characteristics, implementation process, individual characteristics and outer and inner setting is critical to implementation. We have conducted three systematic reviews (n=5315) and semi-structured interviews of postpartum women (n=21) to identify these core components. Evidence synthesis was conducted with the frameworks of PIPE (penetration, implementation, participation, effect) impact metric, TIDieR (Template for Intervention Description and Replication), COMB (Capability, Opportunity, Motivation and Behaviour) and BCT (Behaviour Change Techniques) to identify core components for population impact, intervention delivery, intervention content and behaviour change strategies respectively. PIPE analysis identified few studies reporting penetration and participation and the limited evidence suggest a very low penetration rate. Interventions embedded within existing postpartum services had higher participation rates. TIDieR analysis revealed that lifestyle interventions combining both diet and exercise and delivered by health professionals were more effective. BCT analysis showed that reduction in energy intake was associated with self-regulation skills such as problem-solving, goal-setting, self-monitoring and feedback on behaviour. COMB analysis revealed peer support, involvement of partners, addressing sleep issues, low intensity and flexible delivery, low financial cost, mental health benefits of a healthy lifestyle, enjoyment of healthy lifestyle and promotion of self-care as priorities to address key barriers and facilitators reported by postpartum women. COMB analysis on health professionals revealed the need for upskilling in providing postpartum lifestyle support. These core components will be presented to stakeholders for co-production of interventions for optimising lifestyle and weight in postpartum women.