To address the inter-connected climate and biodiversity crises, it is crucial to understand whether, and if so how, nature-based solutions are perceived to contribute to carbon neutrality, biodiversity, human well-being and justice outcomes. We propose and explore the concept of carbon-smart green infrastructure (carbon-smart UGI) for bridging the policy agendas of climate change mitigation/adaptation and biodiversity conservation, while also accounting for environmental justice. We base our conceptualization of carbon-smart UGI on the findings of a survey distributed among urban residents of Helsinki, Finland. Using both qualitative and quantitative methods, we describe how residents (n = 487) understand carbon-smart UGI, extract clusters of core meanings associated with the concept, and relate these clusters to measures of perceived environmental (in)justice and socio-demographic contexts. In our results, carbon-smartness manifests at different levels of abstraction, agency, and scale, and incorporates community values and concerns attributed to the planning, features, functions, and transformational dimensions of urban green infrastructure. Core meanings associated with carbon-smartness emphasize either actions towards sustainability, carbon neutrality, biodiversity or unfamiliarity towards the concept. Perceived justice concerns and the socio-demographic contexts of the respondents covaried with the meanings associated with carbon-smart UGI. Namely, residents reporting high levels of perceived justice more often highlighted recreation, biodiversity, or other co-benefits than those reporting low levels of justice, while respondents 25 and older supported a more holistic understanding of the concept than those younger than 25. The results highlight the perceived multifunctionality of the urban green and illustrate community perceptions of how it is not only possible, but rather expected, that climate change and biodiversity loss are tackled together in cities. Challenges for implementing carbon-smart UGI include navigating the different meanings associated with the concept and including residents with diverse socio-economic backgrounds during the process. Carbon-smart UGI emerges as a promising boundary object for bridging policy agendas related to carbon neutrality, biodiversity protection, and human well-being that cities can implement when aiming for sustainable, just and socially acceptable transitions towards a good Anthropocene