Born on January 27, 1824, near Greeneville, in Greene County, Tennessee,[1] Key attended the common schools, then graduated from Hiwassee College in 1850 and read law the same year.

[2] He served in the Confederate States Army from 1861 to 1865, during the American Civil War and was promoted to lieutenant colonel of the Forty-third Tennessee Infantry.

[2] Key served as Postmaster General of the United States in the cabinet of President Rutherford B. Hayes from 1877 to 1880.

[1] The only Democrat in Hayes' cabinet, his appointment was in part due to the terms of the Compromise of 1877.

[1] He was confirmed by the United States Senate on May 27, 1880, and received his commission the same day.