After his father's death when he was around ten Grayson's mother married Peter Buell Porter.

In 1847 Grayson left to fight in the Mexican-American War where he arrived as a captain of the artillery.

[5] Grayson fought in many battles in Mexico including the Siege of Veracruz, Battles of Cerro Gordo, Contreras, Churubusco, Molino del Rey, Chapultepec, and the capture of Mexico City.

Because of his long service and military skills, Grayson was quickly appointed a brigadier general in the Confederate Army.

[1] He died soon after on October 21, 1861, in Tallahassee, Florida, at the age of 55, not having fought a single battle during the Civil War.