How do nature-based solutions contribute to biodiversity in cities?

• Global analysis of 185 Nature-based solutions (NbS) cases in 87 cities. • Majority of NbS contribute positively to urban biodiversity. • NbS mostly provide win–win outcomes for biodiversity and human well-being. • We show that evidence is limited to a few NbS types, taxa and metrics. • Comparative studies on biodiversity outcomes of NbS remain lacking. The multifunctional character of nature-based solutions (NbS) in cities, benefiting both biodiversity and human well-being, is gaining increasing attention. Designing multifunctional NbS in cities requires insights in how NbS contribute to biodiversity, since biodiversity supports ecosystem stability and resilience, and benefits for people. While knowledge of urban biodiversity has increased, a comprehensive understanding of how NbS contribute to biodiversity is still lacking. We analyzed the outcomes of 185 urban NbS cases in 87 cities across 33 countries, based on data collected in a systematic literature review. Our results show that 78% of NbS cases contribute positively to improving biodiversity when compared to non-NbS. In some cases, their performance was comparable to that of natural reference sites. Twenty-eight NbS cases evaluating multiple outcomes, beyond biodiversity, predominantly demonstrate win–win solutions for biodiversity and human well-being, although the evidence base remains limited. We showed that current evidence is limited to specific taxa (mostly animals), NbS types (e.g., gardens, forests), and commonly used metrics (e.g., species richness, abundance). We also found that only 39% of cases integrated baseline data, highlighting a lack of comparative studies effectively assessing NbS contributions to biodiversity. Our research provides insights for indicator selection to facilitate the evaluation of NbS for biodiversity and beyond, advancing the understanding of multifunctional NbS, and expanding NbS evaluations to provide accessible information for decision-making and policy.