<p>Extensive evidence indicates that physical activity interventions for middle-aged and older adults are effective in controlled trial settings. However, translating these interventions into real-world public health practice is a complex and dynamic process. Reports highlight a significant gap between scientific evidence and public health practice regarding the implementation of effective physical activity interventions. Real-world implementation is not straightforward; it requires iterative decision-making and continuous alignment across multiple interconnected steps. Although several frameworks exist to guide implementation, many lack practical guidance on how to operationalize them—specifically, ‘what to do’ and ‘how to do it’—especially within complex and evolving settings. This paper draws insights from the comprehensive research project ‘Impactful Implementation: Improving Physical Activity among People Aged over 50’. The project comprised five qualitative and quantitative studies that involved professional stakeholders and end-users. We outline how theory-based implementation frameworks can be operationalized in real-world settings across seven interdependent aspects: (1) defining performance objectives and implementation outcomes, (2) engaging stakeholders, (3) user-centered tailoring, (4) identifying and prioritizing determinants, (5) matching, operationalizing, and verifying implementation strategies, (6) developing an implementation plan, and (7) evaluating implementation. By highlighting the interplay among these aspects and the iterative nature of implementation processes, this paper provides valuable insights for researchers and practitioners aiming to bridge the gap between theory and practice in implementing physical activity interventions in public health.</p>