This paper evaluates life cycle Greenhouse Gas (GHG) emissions of a Seawater Reverse Osmosis (SWRO) desalination plant and assesses its performance under three power supply scenarios. A Life Cycle Assessment (LCA) analysis is conducted for a plant located in Perth, Western Australia (WA). Input and output flows of SWRO plant are based on literature and Perth desalination plants. The Simapro Australian and Ecoinvent databases are used for operational phase Life Cycle Inventory (LCI). An LCI for the construction phase of the plant is developed using economic input–output analysis. Electricity supply scenarios are “100% WA grid”, “100% wind energy” and “92% wind energy plus 8% Photovoltaic (PV) solar energy”. Results indicate that renewable energy powered desalination plants achieve GHG emissions reduction of ∼90% compared to the plant powered by WA grid scenario. For the plant powered by fossil based grid electricity, electricity use in the operational phase is found to be responsible for more than 92% of its GHG emissions. On the other hand, for the plants powered by renewable energy, the highest contribution belongs to chemical use in the operational phase (60%) followed by the construction phase (17%). Indirect emissions due to the electricity consumption in the chemical, wind turbine and PV solar panel manufacturing are found to contribute the lion's share (36–39%) of the life cycle emissions for the renewable energy powered desalination plants. Any improvement in fuel mixes in grid electricity towards cleaner energy sources can be beneficial by reducing impacts associated with upstream electricity use in manufacturing. This work provides the first reference to identify and quantify supply chain contributions to the overall environmental impact associated with renewable energy powered desalination plants.