Born in Mercersburg, Pennsylvania, McCullough moved with his family to Urbana, Illinois.
He served in the 76th Illinois Volunteer Infantry Regiment during the American Civil War.
After the civil war McCullough went to the soldiers school in Fulton, Illinois.
From 1897 to 1913, McCullough served as the Auditor of Public Accounts, the State of Illinois.
McCullough died at his home in Champaign, Illinois after suffering a stroke.