Ocean circulation off the Western Australia coast in the southeast Indian Ocean is dominated by the poleward-flowing Leeuwin Current. Interannual and decadal variability of the Leeuwin Current is to a large extent driven by tropical Pacific climate variability, such that the current is stronger during La Niña events and weaker during El Niño events. Interannual variability of ocean temperature off the Western Australia coast is mostly forced by the Leeuwin Current heat advection and the buffering role of local air-sea heat flux. Unprecedented warm sea surface temperature (SST) anomalies were observed off the west coast of Australia in February–March 2011. Peak SST during a 2-week period were 5°C warmer than normal, causing widespread coral bleaching and fish kills. Understanding the climatic drivers of this extreme event, which we dub “Ningaloo Niño”, is crucial for predicting similar events under the influence of global warming. In this study we use observational data and numerical models to demonstrate that the extreme warming was mostly driven by an unseasonable surge of the poleward-flowing Leeuwin Current in austral summer, which transported anomalously warm water southward along the coast. The unusual intensification of the Leeuwin Current was forced remotely by oceanic and atmospheric teleconnections associated with the extraordinary 2010-2011 La Niña. The amplitude of the warming was boosted by both multi-decadal trends of the Pacific climate toward more La Niña-like conditions and intraseasonal variations in the Indian Ocean.