A unionist, he was a delegate to South Carolina's post-civil war constitutional convention, serving as the body's president, and held federal office.

His father published The American Teacher's Assistant and Self-Instructor's Guide, containing all the Rules of Arithmetic properly Explained, etc.

For the rest of his life, he wrote on a variety of subjects, but specialized in the study of several languages, the Middle Ages, and Freemasonry.

He acquired the Greek, Latin, Hebrew, and continental languages almost unaided, and lectured frequently on the intellectual and moral development of the Middle Ages.

[2] Mackey was a Union sympathizer during the Civil War and in July, 1865, President Andrew Johnson appointed him Collector of the Port of Charleston.