Positive psychology interventions (PPIs) and programs differ markedly in implementation quality. Lower quality implementation is associated with interventions that include multiple components (or PPIs), are delivered across multiple layers (individual, workgroup/ classroom and organisation/school) or agency sites, and include cohorts with heterogeneous or complex needs (e.g., trauma). This paper collectively refers to these interventions as 'complex PPI's' or 'complex programs'. Drawing upon the implementation science literature, we argue that logic modelling represents a method to guide the design and implementation of 'complex' interventions. We describe a growth-focused logic model and implementation methodology (titled intentional practice) that operationalises positive psychology outcomes and processes to support program developers to achieve a balance between fidelity and adaptation. The Resilient Futures program, developed by the South Australian Health and Medical Research Institute (SAHMRI) Wellbeing and Resilience Centre, is described as a case example of the approach. This program represents a large scale and multi-site implementation of a resilience and wellbeing skill-building program for 850 young people from disadvantaged backgrounds with heterogeneous needs. The case study describes how logic modelling and intentional practice consolidated early theory building work to operationalise the intervention at the program level, but also to support multi-site nuancing and translation of the program to individual sites and agency/youth needs. The article argues that logic modelling offers a flexible and evidence-based method for program designers, facilitators and researchers to design and implement complex PPI's or programs. Key considerations for utilising logic models are offered.