The son of Charles "Don Carlos" Percy, (1704–1794), an adventurer from Ireland with pretensions to blood lines of the Dukes of Northumberland, he was born in Alabama in the late 1780s and graduated from Princeton in 1806.
His fellow Princetonian and friend, John Walker, one of the first two senators from Alabama, married Maria's sister Matilda.
Both men built houses on abutting estates in Huntsville and named their sons for each other.
He and Maria named their eldest son John Walker, after his boon companion.
After the war, Colonel Percy, a successful railroad developer, was elected to the state legislature.