Sustainable development is a key feature of national, European Union and global development strategies. The main research goal is to provide evidence on how impactful public policies on environmental sustainability in Portugal are at the regional level, in various policy areas. In this context, this paper analyses the main impacts of the Portuguese Operational Programme for Sustainability and Efficient Use of Resources (PO SEUR 2014–20). The research uses a territorial impact assessment (TIA) methodology (TARGET_TIA) to assess these impacts in five analytic dimensions (economy with low emissions, adaptation to climate change, risk prevention and management, environmental protection and resource efficiency) in the five mainland Portuguese NUTS 2. It concludes that, in overall terms, PO SEUR produced low to moderate positive impacts in all NUTS II and analysed dimensions, but it was particularly positive in measures fostering adaptation to climate change, and less impactful in measures supporting an economy with low emissions and resource efficiency in Portugal. Despite data limitations, the research provided adequate evidence that key public policies supporting environmental sustainability in Portugal are largely ineffective and inefficient in view of their policy goals and allocated funding. To turn this scenario around, the process of project selection needs to undergo significant improvements to better adjust the regional needs on environmental sustainability-related issues to the available funding. Moreover, on a policy strategic level, there needs to be support for a prosperous, modern, competitive and climate-neutral economy in Portugal via concrete actions exploring environmental capital and a green economy in urban areas.