Born around 1555 as the son of Konishi Ryusa, a wealthy medicine merchant in Sakai. Despite his merchant lineage, he trained in martial arts and joined Hideyoshi's personal retinue, rising to prominence. He distinguished himself in Hideyoshi's Kyushu campaign (1587) and was suddenly elevated to daimyo with a 240,000-koku domain in southern Higo Province. Influenced by the successors of Francisco Xavier, he converted to Christianity and took the baptismal name Augustino. In the Imjin War (1592) he commanded the Japanese vanguard and captured Hanseong (Seoul) in barely 20 days. He also participated in the 1597 campaign and served as a peace envoy, but his rivalry with the militant Kato Kiyomasa grew severe. At Sekigahara (1600) he fought as a Western army mainstay alongside Ishida Mitsunari but was defeated. Captured while fleeing, he refused seppuku on religious grounds. In October of the same year, he was beheaded at Rokujo Riverbed in Kyoto alongside Mitsunari and others, at age 45.

Skilled in diplomacy and negotiation from his merchant background, combining martial valor with intellect. A man of conviction who held to his Christian faith until death. His feud with Kiyomasa epitomized the warrior-bureaucrat divide.

His refusal of seppuku out of faith is remembered as a symbol of Christian warriors. His diplomatic efforts during the Korean campaigns remain an important chapter in early modern Japan-Korea relations.