In an era of constant technological development and advancements, the shift towards becoming interconnected through globalization proposes an unpredictable and complex ecosystem for organizations to navigate in a rapid manner. Placed within this dynamic environment, the role of design has also become challenged to adapt and propose alternate ways within systemic structures, specially dedicated for innovative service design deliveries for sustainable and resilient futures. By integrating complexity theory and systems thinking into service design, the Green Deal can foster innovative approaches that are better equipped to address the challenges of today, ultimately contributing to a more sustainable and equitable future. Thus, this paper explores how complexity theory can be applied to service design to better understand and navigate challenges posed by green transition. The paper explores the theory of complexity theory and systems thinking as foundational aspects for representing a conceptual approach for responding to the complex nature of environmental and societal systems. The methodology reviews the complexity theory and its relationship with the contemporary service ecosystem, with regard to the systems theory to further estimate the key factors of service design complex adaptive ecosystems. The findings argue a holistic view that adopts a systems-thinking approach to understand the interconnectedness of environmental, economic, and social factors. The paper proposes key factors of service design to non-linear system trajectories emerging as a new research spectrum for strategic design approaches for sustainability.