He attended public schools and American Temperance University in Harriman before graduating from United States. Grant University in Athens, Tennessee, in 1906. He studied law, was admitted to the bar in 1903, and entered the practice of law in Jellico in his native Campbell County, Tennessee.
In Campbell County, Jennings served as county superintendent of public instruction in 1903 and 1904, and county attorney from 1911-1918. In 1918 he became special assistant to the Attorney General of the United States and judge of the second chancery division of Tennessee. He resigned the judgeship July 1, 1923, and moved to Knoxville, Tennessee, where he continued the practice of law.
He was a delegate to the Republican National Conventions in 1912, 1936, and 1944.
In 1939, Jennings was elected to Congress as a Republican, filling the vacancy caused by the death of J. Will Taylor. He took office on December 30, 1939.
He was elected to a full term in the 77th Congress and was re-elected to the four succeeding Congresses. In 1950 Howard Baker, Senior defeated him in his bid for renomination, so he ended his Congressional service January 3, 1951.
After leaving Congress, he resumed the practice of law.
Jennings died in Knoxville on February 27, 1956 and is interred at Highland Memorial Cemetery.
Member Jennings, O’Neil & Jarvis, Knoxville, since 1930. Elected to 76th Congress, 2d Tennessee District, December 1939, to fill unexpired term of J. Will Taylor. Member American, Knox County, Tennessee bar associations.
Mason, Elk, Junior Order American Mechanics.
Married Pearnie Ethel Hamby, September 16, 1906. Children: Ethel (Mistress Martin South. Coykendall), Katherine (Mistress Nowland Van Powell), Helen.