Biochar is suggested as a soil amendment to improve salt-affected soil properties for crop productivity and decrease soil salinity. However, the heterogeneity among biochar experiments in terms of biochar and soil properties and experimental conditions makes it difficult to compare and extrapolate results from different studies. A statistical meta-analysis was undertaken with the aim of evaluating the impacts of biochar on crop productivity and soil salinity in salt-affected soils. The results showed a statistically significant benefit of biochar application to salt-affected soils on crop productivity. The application rate of 40-50 t/ha (41%), C/N ratio of 40-60 (33%), pyrolysis temperature of 450-550 °C (28%) and pH of 7-8 (30%) of biochar yielded the greatest (positive) effects on crop productivity and did not cause an increase in soil salinity in salt-affected soil. With regard to climate analyses, biochar application had the greatest (positive) effects on crop productivity and the greatest (negative) effects on soil salinity at mean annual temperature (MAT) <10 °C (30%), mean annual precipitation (MAP) <400 mm (33%) and MAT <10 °C (-9%), MAP< 400 mm (-9%), respectively. This suggests that the crop productivity increase may be due to an improvement in soil temperature and water retention and a decrease in soil salinity. The greater (positive) effects on crop productivity with regard to soil analyses were seen at pH >8 (24% to 25%), salinity >5 (32% to 60%), and sulfate-dominated (35%) and soda-dominated (26%) saline soils. The greater (negative) effects on soil salinity with regard to soil analyses were seen at salinity >5 (-9% to 22%), and sulfate-dominated (-35%) and soda-dominated (16%) saline soils. This suggests that the crop productivity increase may be due to a decrease in soil pH and salinity in sulfate-dominated or soda-dominated saline soils. A statistically significant increase in the productivity of cash crops and rice was found in salt-affected soils treated with biochar, but soil salinity also increased. A statistically significant increase in crop productivity by biochar was seen in the salt-affected soils with the addition of inorganic fertilizer and no fertilizer compared to the absence of biochar. This meta-analysis provides the first quantitative review of the effect of biochar on crop productivity and soil salinity in salt-affected soil, which is critical for developing engineered biochar to restore salt-affected soil and promote food security.