Present study examined the influence of high-temperature stress and different biochar and phosphorus (P) fertilization treatments on the growth, grain yield and quality of two rice cultivars (IR-64 and Huanghuazhan). Plants were subjected to high day temperature-HDT (35 °C ± 2), high night temperature-HNT (32 °C ± 2), and control temperature-CT (28 °C ± 2) in controlled growth chambers. The different fertilization treatments were control, biochar alone, phosphorous (P) alone and biochar + P. High-temperature stress severely reduced the photosynthesis, stomatal conductance, water use efficiency, and increased the leaf water potential of both rice cultivars. Grain yield and its related attributes except for number of panicles, were reduced under high temperature. The HDT posed more negative effects on rice physiological attributes, while HNT was more destructive for grain yield. High temperature stress also hampered the grain appearance and milling quality traits in both rice cultivars. The Huanghuazhan performed better than IR-64 under high-temperature stress with better growth and higher grain yield. Different soil fertilization treatments were helpful in ameliorating the detrimental effects of high temperature. Addition of biochar alone improved some growth and yield parameters but such positive effects were lower when compared with the combined application of biochar and P. The biochar+P application recorded 7% higher grain yield (plant(-1)) of rice compared with control averaged across different temperature treatments and cultivars. The highest grain production and better grain quality in biochar+P treatments might be due to enhanced photosynthesis, water use efficiency, and grain size, which compensated the adversities of high temperature stress.