Design for Sustainability Transition (DfST) is gaining popularity in both academia and practice, seeking to guide socio-technical systems toward more sustainable futures through design but remaining a high-level approach that is difficult to evaluate. The authors also disagree on the designer’s role during the transitions, leaving it open to exploration. Organisations considered a socio-technical system play a crucial role in solving the climate crisis we are experiencing and need to be guided through change. Working on employees and their practices makes it possible to initiate a snowball effect capable of triggering the necessary cultural change. The Design-Led Innovation approach can be a valuable guide in the cultural transformation of companies, connecting strategic aspects with more pragmatic ones, such as products or services solutions. This also suggests the figure of the Design Innovation Catalyst as a change agent to facilitate the introduction of design as a driver of change. This paper proposes a Conceptual Framework based on Design-Led Innovation and Social Practice Theory to guide the sustainable transition and evaluate the change brought to individuals' practices. Through a 12-month collaboration with an Italian secondary packaging company, it was possible to test the framework and its impact on design-as-practice. The results consolidate the validity of Design-Led Innovation for Sustainable Transition, showing its potential and limitations. The role played by the Design Innovation Catalyst proves to be crucial in facilitating transition and leading to changes in practices.