Agriculture is under significant pressure to meet current and future food demands. Food consumption growth and climate change push the system to produce more food with the same resources. Irrigation is a key strategy to producing higher yields but current practices are already consuming non-renewable water, threatening the natural and human ecosystem. Desalination – the conversion of saltwater from to freshwater – could help ease constraints on irrigation resources, eliminate unsustainable withdrawals and improve yields in a more difficult climate for food producers (for example in increasingly drier regions). However the extent to which desalination can be deployed, and its associated impacts at a global level is largely unquantified. Using data from 172 countries, We estimate the global demand for desalinated irrigation water in 2050 accounting for climate change and varying blue water availability. We assume this water is used to replace both unsustainably sourced freshwater and to meet irrigation requirements under climatic changes. We assess its cost, energy requirement and the brine produced (an environmental impact from desalination). Results indicate that desalinated water could sustainably feed an additional 500 million to 1 billion people when replacing unsustainable blue water withdrawals within the current system and up to 3.5-5 billion people when providing the water resources to close yield gaps. The annual cost of water is significantly higher than current irrigation at 160-2000 billion euros. The use of desalination at a global scale is unlikely due to prohibitive costs and energy requirements. The feasibility of desalination increases with future technological advancements, increasing water scarcity, decreasing costs, and renewable energy integration. However, challenges such as brine disposal and socio-economic constraints need to be solved. We anticipate that desalinated irrigation is looked at as a niche pathway to provide necessary water resources next to storage fed irrigation and irrigation water application efficiency improvements.