E-methanol is considered one of the most cost-effective and sustainable solutions for the decarbonization of naval applications, and its combustion in dual-fuel mode could play a significant role in transitioning marine transportation toward sustainable solutions. Under the framework of the Horizon UPTOME project, an unmanned power-to-methanol production plant has been developed that takes advantage of CO2 point sources (e.g. biogas from wastewater treatment plants) and converts it into methanol using green hydrogen and renewable energy sources for its operation. The objective of this study is to investigate the environmental performance of marine transportation related to the e-methanol produced and to identify the weaknesses and barriers of the process route with the aforementioned production plant, using life cycle analysis (LCA) methods. The system boundaries were defined as ‘Cradle-to-grave’, including hydrogen production and methanol synthesis within the unmanned plant, and methanol utilization in dual fuel mode with MGO, as a maritime fuel. Methanol production data were derived from measurements of the pilot plant operation conducted during the project and supplemented with literature data for hydrogen production and methanol final use. To perform the LCA, the OpenLCA software and the Ecoinvent database were utilized. To identify the environmental benefits of methanol production and use as a marine fuel, the environmental impacts of methanol propulsion on ships have been compared to fossil and other alternative fuels. The production and utilization of methanol in dual fuel mode with MGO can reduce Global Warming Potential by 58% and 68% compared to LNG and MGO, respectively.