Inaba Masakatsu was the eldest son of Kasuga no Tsubone, the wet nurse to shōgun Tokugawa Iemitsu.
In 1624, he received a 5000-koku estate in Makabe District, Hitachi Province, which, added to his existing holdings, propelled him past the 10,000 koku mark to become a daimyō.
Kakioka Domain in Shimōsa Province was created to be his title.
However, on the death of his father Inaba Masanari in 1628, Masakatsu became head of the Inaba clan, and inherited his father's position as daimyō of Mōka Domain, at which time Kakioka Domain was abolished.
In 1632, he was assigned to assist Katō Tadahiro in the reconstruction of Kumamoto Castle.