Populations in high-density urban areas are exposed to higher levels of heat stress in comparison to rural areas. New spatially explicit approaches that identify highly exposed and vulnerable areas are needed to inform current urban planning practices to cope with heat hazards. This study proposes an extreme heat stress risk index for Dublin city across multiple decades (2020s-2050s) and for two representative concentration pathways (RCPs). In order to consider the interactions between greenhouse gas emissions and urban expansion, a climate-based urban land cover classification and a simple climate model have been combined to compute air temperature values accounting for urban heat island effect. This allowed the derivation of an improved hazard indicator in terms of extreme heat stress which, when integrated with information on current levels of vulnerability (i.e., socioeconomic factors assessed using principal component analysis (PCA), provides a heat hazard risk index for Dublin city at a fine spatial scale. Between the 2020s and 2050s, urban areas considered at highest risk are expected to increase by about 70% and 96% under RCP 4.5 and 8.5 respectively. For the 2050s, enhanced levels of heat risk under the RCP 8.5 scenario are particularly visible in the core city centre and in the northern and western suburbs. This study provides a valuable reference for decision makers for urban planning and provides an approach to help prioritise management decisions for the development of heat resilient and sustainable cities.