Sogō Senmatsumaru lived during the Azuchi-Momoyama period from Tenshō 3 (1575) to Tenshō 17 (1589).
His father, Masayasu, obeyed Toyotomi Hideyoshi. In 1586, during the Battle of Hetsugigawa, Senmatsumaru, had not yet met Toyotomi Hideyoshi. Prior to dying, Masayasu told his retainers that if he were to die, to have his son meet Hideyoshi so the Sogō family would continue. After his death, however, his landholdings were seized. The fief was then granted to Ikoma Chikamasa where Senmatsumaru was raised with only 3,000 koku for small expenses.
In the seventh month of 1589, Senmatsumaru met Hideyoshi. Pleased with Senmatsumaru’s maturity, Hideyoshi expressed disapproval toward Chikamasa and his nephew, Ōtsuka Uneme, that only 3,000 koku had been allocated to Senmatsumaru. However, after Hideyoshi returned to his home province, Senmatsumaru soon died of illness. The sudden death gave rise to rumors that the Ikoma clan had poisoned him. The surviving family members and local residents expressed their grief in worship at his grave.