Sorghum is a major cereal food worldwide, and is considered a potential source of minerals and bioactive compounds. Its wide adaptive range may cause variations in its agronomic traits, antioxidant properties, and phytochemical content. This extensive study investigated variations in seed characteristics, antioxidant properties, and total phenolic (TPC) and flavonoid contents (TFC) of sorghum collected from different ecological regions of 15 countries. The antioxidant potential of the seed extracts of various sorghum accessions was determined using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azinobis 3-ethylbenzothiazoline-6-sulfonate (ABTS) radical scavenging assays. Significant variations in TPC were observed among the sorghum accessions. All 78 sorghum accessions used in this study exhibited significant variations in TFC, with the lowest and highest amount observed in accessions C465 and J542, respectively. DPPH scavenging potential of the seed extracts for all the accessions ranged from 11.91 ± 4.83 to 1343.90 ± 81.02 µg mL-1. The ABTS assay results were similar to those of DPPH but showed some differences in the accessions. Pearson's correlation analysis revealed a wide variation range in the correlation between antioxidant activity and TPC, as well as TFC, among the sorghum accessions. A wide diversity range was also recorded for the seed characteristics (1000-seed weight and seed germination rate). A dendrogram generated from UPGMA clustering, based on seed traits, antioxidant activity, TPC, and TFC was highly dispersed for these accessions. Variations among the accessions may provide useful information regarding the phytoconstituents, antioxidant properties, and phytochemical contents of sorghum and aid in designing breeding programs to obtain sorghum with improved agronomic traits and bioactive properties.