Pigeon pea (Cajanus cajan) is an important legume species that produces seeds that are rich in phenolic compounds and dietary nutrients. The aim of the present study was to evaluate the agricultural characters, phenolic and nutritional contents, and antioxidant capacities of seeds from 82 pigeon pea germplasms cultivated in the Republic of Korea. The accessions exhibited compact (24.39%), semi-spreading (74.39%), or spreading (1.22%) growth habits and determinate (89.02%), indeterminate (8.54%), or semi-determinate (2.44%) flowering patterns. Days to 75% maturity ranged from 30 to 72 d, and yield per plant ranged from 6.00 to 148.60 g. Meanwhile, total phenolic, crude protein, crude fiber, and dietary fiber contents ranged from 16.42 ± 0.62 to 29.67 ± 0.43 mg gallic acid equivalent per g of dried extract, from 16.76 ± 6.74% to 22.61 ± 0.05%, from 4.70 ± 0.24 to 8.63 ± 0.02%, and from 12.98 ± 0.71 to 33.19 ± 1.50%, respectively. In addition, DPPH radical-scavenging capacity ranged from 1.61 ± 0.10 to 16.04 ± 2.30 mg ascorbic acid equivalent per g of dried extract, and Trolox equivalent antioxidant capacity ranged from 3.03 ± 0.86 to 42.24 ± 0.72 mg Trolox equivalent per g of dried extract. Phenolic content was correlated with both DPPH radical-scavenging capacity (r = 0.63) and Trolox equivalent antioxidant capacity (r = 0.29). Nine accessions (IT170290, IT170291, IT170270, IT170276, IT170379, IT170386, IT170388, IT170418, and IT170340) exhibited early maturity, compact and erect growth habits, and above average antioxidant activities and phenolic and protein contents. In addition, accessions IT170290 and IT170291 were especially promising pigeon pea germplasms to grow, owing to various favorable characteristics (e.g., high yield and dietary fiber content). Hence, these accessions could be useful cultivars to the Republic of Korea if considered in future agricultural systems.