Lt. Col. David McKendree Key, 43rd Tennessee Infantry, CSA, served in all three branches of the U. S. Federal Government post war, see:

David M. Key
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David McKendree Key
DMKey-PostmasGener.jpg
27th United States Postmaster General
In office
March 12, 1877 – June 2, 1880
Preceded by James N. Tyner
Succeeded by Horace Maynard
United States Senator
from Tennessee
In office
August 18, 1875 – January 19, 1877
Preceded by Andrew Johnson
Succeeded by James E. Bailey
Personal details
Born January 27, 1824
Greeneville, Tennessee, U.S.
Died February 3, 1900 (aged 76)
Chattanooga, Tennessee, U.S.
Political party Democratic
Spouse(s) Elizabeth Lenoir Key
Alma mater Hiwassee College
Profession Lawyer, Politician
Military service
Allegiance Confederate States of America Confederate States of America
Service/branch Confederate States Army
Rank Confederate States of America Lieutenant Colonel.png Lieutenant Colonel
Unit Tennessee 43rd Tennessee Regiment
Battles/wars American Civil War
David McKendree Key (January 27, 1824 – February 3, 1900) was a Democratic U.S. Senator from Tennessee from 1875 to 1877 as well as the U.S. Postmaster General under President Hayes, and a United States federal judge.

Biography
Key was born in Greene County, Tennessee, the son of Reverend John and Margaret (Armitage) Key. In 1826 the family moved to Monroe County where Key was reared, graduating from Hiwassee College in 1850. He selected the legal profession as his vocation through life, and the same year of his graduation he read law to be admitted to the bar. He practiced law for two years at Madisonville, then worked for a short time in Kingston. He moved to Chattanooga in February 1853. He married Elizabeth Lenoir in 1857, and fathered nine children.

When the Civil War broke out, Key enlisted in the Forty-third Confederate Tennessee Regiment of Infantry, served until the close of the war, and was mustered out as a lieutenant colonel. He then resumed the practice of law in Chattanooga until 1868.

Key was a member of the Tennessee state constitutional convention of 1870, which composed the basic instrument of government of the state still in effect. In August of the same year, he was elected chancellor of the Chattanooga (3rd) division, defeating the Republican incumbent, Daniel C. Trewhitt. He maintained his chancellorship during an unsuccessful campaign for the U.S. House in 1872, but resigned in 1875 to accept the appointment by Tennessee Governor James D. Porter to the vacant Senate seat created by the death of Andrew Johnson.

Defeated in the next senate election in the Tennessee General Assembly, Key was appointed Postmaster General in 1877 by President Hayes, and served until August 25, 1880. His appointment as Postmaster General was part of the Compromise of 1877, implemented to ensure there was Democratic power in the Republican cabinet. Key's work as Postmaster General is harshly criticized by Mark Twain in The Autobiography of Mark Twain.

On May 19, 1880, Key was nominated by President Hayes to a joint seat on the United States District Court for the Middle District of Tennessee and the United States District Court for the Eastern District of Tennessee, vacated by Connally F. Trigg. Key was confirmed by the United States Senate on May 27, 1880, and received his commission the same day. Key retired from the bench on January 21, 1895. He died in Chattanooga in 1900 and is buried there.