Australian cotton (Gossypium hirsutum L.) farmers are adopting canopy temperature (Tc)-based irrigation scheduling as a decision support tool to improve on-farm production. High N supply, characteristic of the high-yielding, furrow-irrigated cotton system of Australia, might alter cotton Tc with implications for irrigation. We examined growth, physiological, and biochemical traits and changes in Tc of well-watered and water-stressed cotton plants supplied with high to excessive levels of N under glasshouse conditions. We also examined Tc, lint yield, and fiber quality of furrow-irrigated cotton crop supplied with high N. In the glasshouse and under well-watered conditions, high N supply stimulated plant growth and increased stomatal conductance and photosynthesis, resulting in cooler Tc. Under water deficit stress, high N also stimulated growth, increasing plant water demand and thus vulnerability to water stress, which manifested as warmer Tc. Water-stressed plants supplied high N also showed reduced stomatal conductance, lower leaf water potential, and greater accumulation of leaf and xylem sap abscisic acid. Furrow-irrigated crops supplied higher N also had higher Tc, but there was no gain in lint yield and fiber quality. The influence of high N on cotton Tc suggests that the need for accurate and reliable Tc-based irrigation scheduling is paramount.