In this paper the REACT-DECARB energy planning platform, designed to assist with the assessment of decarbonisation scenarios for islands’ electricity grids, is fully presented and applied to eight (8) EU islands. The scenarios were developed in the context of a Horizon 2020 EU project employing a renewable energy production forecasting and an optimisation mixed-integer linear programming model. The platform employs energy and economic modules, life-cycle assessment and multi-criteria decision analysis to facilitate the integrated evaluation of scenarios and enables decision makers to fully grasp the technical, environmental, economic and social aspects of energy systems’ decarbonisation. Results indicate that island electrical autonomy should be considered with caution and can be a valid option only if cost criteria are not prioritised. Further, it was determined that seeking autonomy in countries with low carbon costs for electricity production may be not be environmentally beneficial. A number of inter-island comparisons have been made and have shown that the REACT-DECARB platform can assist planners and decision-makers to identify the best available scenarios, define the sensitivity issues with respect to the criteria weights and, together with local communities, come to a common ground in order to establish a roadmap for the transition towards a decarbonised energy future for islands.