Innovation ecosystems today are under more pressure than ever to not only improve technology but also solve social and environmental problems. This study, informed by the Triple Helix Theory and Public Value Theory, formulates and evaluates a multilevel framework elucidating how collaboration across universities, industry, and governments can produce sustainable and socially beneficial innovation outcomes. The model analyses the contributions of Cross-Helix Knowledge Co-Creation Intensity (CKCI) and Public Value Orientation of Innovation (PVOI) to the development of Network Structural Diversity (NSD), which subsequently enhances Sustainable Innovation Capabilities (SIC). The study utilizes data from pivotal innovation sectors in the US and UK, demonstrating that SIC is a strong predictor of both Societal Impact Performance (SIP) and Triple Helix Sustainability Synergy (THSS). A serial mediation pathway from CKCI and PVOI through NSD and SIC is established, demonstrating that collaborative knowledge and public value orientation collectively yield beneficial social outcomes. The moderating effect of Policy Environment Dynamism (PED) on the relationship between SIC and SIP was not significant, indicating that robust internal capacities can still influence social outcomes in unstable policy environments. This study offers theoretical and practical insights for businesses aiming to develop inclusive, mission-oriented, and resilient innovation ecosystems.