Large ash plumes emitted by the 2019–2020 Australian wildfires were associated with a widespread phytoplankton bloom in the iron‐limited Pacific sector of the Southern Ocean. In this study, we used satellite observations and aerosol reanalysis products to study the regional phytoplankton community response to wildfire emissions. The bloom was stimulated by pyrogenic iron fertilization and coincided with elevated cellular pigment concentrations, increased photochemical efficiency, and apparent community structural shifts. Physiological anomalies were consistent with previously observed phytoplankton responses to iron stress relief and persisted for up to 9 months. Supported by a regional iron budget, we conclude that the bloom was sustained by iron recycling and episodic inputs of pyrogenic and dust‐borne mineral iron. The continuous regeneration of iron was likely facilitated by the bloom's large size, mitigating edge dilution effects, as well as enhanced bioavailability of pyrogenic and mineral iron due to atmospheric and chemical processing during long‐range transport. Plain Language Summary Phytoplankton are the “plant” plankton at the base of the ocean food chain. Phytoplankton growth in the Southern Ocean is limited by the availability of iron. Deserts and wildfires are two important sources of iron‐bearing particles that can be transported over long distances and deposited on the ocean surface, causing increased phytoplankton growth and species changes. In this study we used observations from satellites to study the physiological response of a large phytoplankton bloom stimulated by emissions from the 2019–2020 Australian wildfires. We found the cells became richer in pigments, and more efficient in their photosynthesis. The changes are directly attributable to wildfire emissions and correspond with previously observed phytoplankton responses to iron fertilization experiments and natural fertilization by dust, volcanic ash, and upwelled iron from the deep ocean. The phytoplankton response lasted almost half a year after wildfire particles stimulated the bloom. We attribute the prolonged response in part to iron recycling, re‐supplying dissolved iron inside the bloom, and to additional deposition of wildfire emissions and dust. Key Points 2019–2020 Australian wildfire emissions stimulated phytoplankton community responses consistent with iron fertilization Physiological anomalies lasted 9 months and were sustained by iron recycling and atmospheric iron supply by dust and wildfire emissions Atmospheric processing of wildfire emissions likely increased the solubility of pyrogenic iron, amplifying its effect on the phytoplankton