Named for his grandfather, Isaac Moses, Jr. was one nine children born to Joshua and Sara Rodriguez Brandon Moses. His siblings included twin brother Moses, Abraham, Israel, Lionel, Benjamin and Joseph. The kids were brought up in New York, and Isaac, like his father went into the East India trade.

During the Civil War he achieved the rank of lieutenant colonel, serving as adjutant general of the Third Army Corps of the Army of the Potomac. After the war he spent some time in Galveston, Texas, living there through the yellow fever epidemic of 1968 to which General Charles Griffin succumbed while staying as a guest at Moses’ house. He died unmarried in New York.