Hong Kong's Transitional Housing Programme demonstrates how SDG 11 and SDG17 catalyse affordable housing at unprecedented scale and speed. In five years, over 21,000 units—86% using Modular Integrated Construction (MiC)—were delivered by mobilising government, 20 NGOs, private land donors, consultants, contractors, and manufacturers into a public–private–people ecosystem producing dignified homes and supportive neighbourhoods. This global-leading societal participation achieved the fastest relocatable building delivery, repurposing idle land and coordinating cross-department infrastructure support. The programme operationalised SDG11 and SDG17 through co-creation rather than mere coordination: NGOs functioned as builders and operators; private developers contributed underutilised sites at nominal cost; manufacturers, consultants, and charities jointly solved technical and social challenges. This integrated approach was essential - no single actor could have achieved this alone. Government's agility and funding model enabled responsive partnerships; NGO networks activated grassroots trust; and private sector innovation accelerated MiC adoption via learning-by-doing, overcoming regulatory hurdles and positioning Hong Kong as a global modular leader. Comparative analysis with Vancouver and London reveals that centralised tenant systems, sustainable operational funding, and design standardisation compress delivery timelines while preserving local context. Hong Kong's whole-of-society model offers a replicable blueprint: co-design governance balancing government oversight with NGO autonomy; establish transparent benefit-sharing mechanisms; standardise processes to reduce transaction costs; plan early for unit circularity and reuse. Persistent challenges—short site tenures, uneven NGO capacity, low cross-project standardisation—demonstrate that partnerships require sustained commitment and policy alignment. This presentation, stemming from a Strategic Public Policy Research, consolidates the lessons learnt and operationalises SDG11 and SDG17 through structural interdependence: shared problem-framing, aligned incentives, distributed accountability, and genuine power-sharing. By documenting both triumphs and pain points, this work offers cities a transferrable partnership governance model for scaling dignified, affordable housing through multi-sector collaboration—transforming emergency responses into durable, sustainable built environment practices aligned with global development goals.