In recent years, several researchers have studied the potential use of ammonia (NH3) as an energy vector, focused on the techno-economic advantages and challenges for full global deployment. The use of ammonia as fuel is seen as a strategy to support decarbonization; however, to confirm the sustainability of the shift to ammonia as fuel in thermal engines, a study of the environmental profile is needed. This paper aims to assess the environmental life cycle impacts of ammonia-based electricity generated in a combined heat and power cycle for different ammonia production pathways. A cradle-to-gate assessment was developed for both ammonia production and ammonia-based electricity generation. The results show that electrolysis-based ammonia from renewable and nuclear energy have a better profile in terms of global warming potential (0.09–0.70 t CO2-eq/t NH3), fossil depletion potential (3.62–213.56 kg oil-eq/t NH3), and ozone depletion potential (0.001–0.082 g CFC-11-eq/t NH3). In addition, surplus heat for district or industrial applications offsets some of the environmental burden, such as a more than 29% reduction in carbon footprint. In general, ammonia-based combined heat and power production presents a favorable environmental profile, for example, the carbon footprint ranges from −0.480 to 0.003 kg CO2-eq/kWh.