Accelerating urbanisation has led to wider adoption of the smart‑city (SC) model in pursuit of sustainable development (SD). This study examines how urban digital platforms that integrate sensing, data governance, analytics, and participatory tools translate citizen inputs into sustainability outcomes and green‑job (GJ) formation. A comparative multiple‑case study is conducted across Amsterdam, Athens, Seville, and Osaka. Evidence is compiled from municipal strategies, platform portals and open‑data catalogues, programme evaluations, technical and procurement documentation, and peer‑reviewed sources. Cross‑case synthesis and pattern matching are applied to assess how platform features (open application programming interfaces—APIs, standards, privacy and accountability arrangements) and participation modalities (reporting, co‑design, participatory budgeting) influence measurable outcomes in energy, mobility, circularity, and air quality, as well as associated GJ pathways. The results indicate that (1) platforms with transparent pipelines from citizen input to implementation show stronger links to SD indicators and ecosystem activity; (2) robust data‑governance mechanisms broaden participation and enhance the durability of results; and (3) close alignment between platform analytics and procurement/operations fosters local green‑and‑digital employment. Implications for platform design and governance are outlined, together with research needs on participation quality, impact measurement, and transferability across institutional contexts.