After Hideyoshi's death in 1600, he participated in the subjugation of Kagekatsu UESUGI following one of the Council of Five Elders, Ieyasu TOKUGAWA, and when one of the five major magistrates, Mitsunari ISHIDA raised his forces while Ieyasu was away, Katsutoyo joined the eastern forces.
秀吉の死後の慶長5年（1600年）には五大老の徳川家康に従って会津の上杉景勝の討伐に参加し、家康の留守中に五奉行の石田三成らが挙兵すると東軍に与している。