With the increasing demand for land to accommodate residential, industrial, and commercial development within our cities, the preservation and management of our green spaces and biodiversity in the urban landscape is critical. This paper examines the complex issue of creating sustainable green systems and protecting biodiversity within the built environment. Existing green spaces and biodiversity are experiencing pressure from competing land uses and human activities predominantly in our capital cities. Our research focuses on preservation and management of green spaces and biodiversity in metropolitan Melbourne under the umbrella of the Melbourne 2030 planning strategy. We use the City of Darebin, one of thirty-one local government areas comprising metropolitan Melbourne as case study in order to develop urban green system scenarios incorporating biodiversity conservation. A geographical information system (GIS) based planning support system (PSS) tool is used to construct urban green system scenarios for the City of Darebin. Specifically, the land suitability module of the What if? GIS-based PSS is used to bring together a number of spatial datasets used to formulate the urban green systems scenarios. The datasets entered into the PSS encompass a wide range of cultural and natural assets data layers including: existing open spaces, waterways, threatened fauna and flora, ecological vegetation covers, registered cultural heritage sites, and existing land parcel zoning. The results of our analysis is an open space biodiversity index for the City of Darebin, which can be used to assist in assessing future land use development applications. It is recommended that such open space biodiversity indexes should be used to define and preserve green systems in the Australian urban environment.