The additions of biochar and inorganic fertiliser to agricultural soils have been reported to enhance soil fertility and crop production under rainfed and irrigation conditions. However, it is unclear how biochar improve the growth, yield, irrigation and crop water use efficiency of a field grown maize under deficit irrigation. The objective of this study is to determine the main and interactive effects of biochar and fertiliser on the maize growth, yield, crop water use efficiency (CWUE) and irrigation water use efficiency (IWUE) under deficit irrigation, which has been scarcely studied. Therefore, a field experiment which consisted of factorial combination of Irrigation (100% Full Irrigation (FI), 80% FI and 60% FI), biochar (0 and 20 t/ha) and fertiliser (0 and 300 Kg/ha) was conducted over two growing seasons. The 100% FI, 80% of FI and 60% of FI received 1, 0.8 and 0.6 of the estimated irrigation need required to bring the soil water to field capacity, respectively. Effect of the soil amendments were determined on the crop evapotranspiration (water use), soil hydrophysical and chemical properties. Maize growth parameters were determined weekly while the yield components were determined at harvest. Results showed that the application of the soil amendments improved the soil hydro-physical, chemical properties, and water use by maize plant which consequently resulted in increased maize growth, yield, IWUE and CWUE under all irrigation treatments. Combined addition of the soil amendments gave significant (P < 0.05) improvement on the maize grain yield, biomass yield, CWUE and IWUE compared to the unamnded plot in all irrigation treatments. Also, insignificant interaction occurred between biochar and irrigation on maize productivities. Therefore, amending soil with biochar under limited water supply might be a novel approach for enhancing maize yield and water use efficiencies by minimizing the negative impact of drought stress.