Born in Loraine, Texas, Mahon received a Bachelor of Arts degree from McMurry University in 1939 and a Bachelor of Laws from the University of Texas School of Law in 1942.
He was in the United States Army Air Corps from August 1942 to November 1945 and became a captain.
[1] Mahon was nominated by President Richard Nixon on June 23, 1972, to a seat on the United States District Court for the Northern District of Texas vacated by Judge Joe Ewing Estes.
He was confirmed by the United States Senate on June 28, 1972, and received his commission on July 3, 1972.
Mahon served in that capacity until his death on December 3, 2005, in Fort Worth, Texas.