Three peanut (Arachis hypogaea L.) cultivars were grown under optimal field conditions in two environments in subtropical Australia contrasting primarily in night temperature. Mean minimum temperatures during the growing season were 16.7 °C (Kingaroy, cool) and 20.1 °C (Bundaberg, warm). Dry matter production was similar in both environments, but pod yields were slightly higher with warm nights (P < 0.05). This occurred despite large differences in rates of development between environments, with plants of all cultivars in the warm night environment maturing 23 to 24 d earlier. Accumulation of energy-corrected dry matter was highly correlated with cumulative intercepted shortwave solar radiation. There were no significant differences among cultivars in the rate of accumulation of energy-corrected dry matter per unit of intercepted shortwave radiation (radiation-use efficiency; RUE, g MJ−1) in either environment. Data were pooled within environments, with RUE in the warm environment 39% higher than with cool nights. This higher RUE in the warm nights occurred despite poorer radiation distribution within the canopy and lower specific leaf N. A subsequent glasshouse study with ‘Early Bunch’ peanut compared growth and RUE at day/night temperature regimes of 33/23 °C and 33/17 °C, and confirmed the role of night temperature in determining RUE. Cool night effects were associated with increased specific leaf weight and lower stomatal conductances. Both effects were evident from 7 d after start of treatments, but differences were never greater than ≈ 10%. Analysis of published RUE data for Early Bunch peanut from tropical and subtropical environments collectively showed a highly significant (P < 0.01) negative linear relationship between RUE and night temperature.