A major challenge in volcanology is determining the factors that control the frequency and magnitude of eruptions at hazardous caldera volcanoes. Understanding the critical sequence of events that may lead to future eruptions is vital for volcanic monitoring and risk assessment. Here we use magma chemistry and mineral diffusion modeling to interpret the magmatic processes and time scales involved in the youngest three eruptions (2.15–1.7 ka) from Taupo volcano (New Zealand), which peaked with the voluminous A.D. 232 eruption. Of the rhyolites erupted since ca. 12 ka, the <2.15 ka magmas have the lowest whole-rock SiO2 content and reversely zoned crystals, yet with high-SiO2 melt inclusions. Mineral zonations and compositional shifts reflect a 30–40 °C temperature increase over the immediately preceding (>2.75 ka) rhyolites that were tapped from the same magma reservoir. Orthopyroxene Fe-Mg diffusion time scales indicate that the onset of rapid heating and priming of the host silicic mush occurred <120 yr prior to the <2.15 ka eruptions, with subsequent melt accumulation occurring in only decades. Elevated mafic magma supply to the silicic mush pile, rapid melt accumulation, and high differential tectonic stress built up and culminated in the ∼105 km3 A.D. 232 eruption, one of the largest and most violent Holocene eruptions globally. These youngest eruptions demonstrate how Taupo’s magmatic system can rapidly change behavior to generate large eruptible melt bodies on time scales of direct relevance to humans and monitoring initiatives.