Born in San Antonio, Texas, Sparks grew up in Miami, Arizona, where his father worked for a copper mining company. In 1935, after unsuccessfully seeking jobs in the shipyards of Corpus Christi, Texas and San Francisco, he enlisted in the U.S. Army.
In a ten-year army career, which included the December 1941–August 1945 period of World War II, Sparks rose to the rank of colonel. Upon returning to civilian life, he attended the University of Colorado Law School, graduating in 1947. After opening a law practice in Delta, Colorado, he was elected district attorney there, running as the Democratic Party candidate. Following his reelection loss in 1952, Governor Ed Johnson appointed him to fill an unexpired term on the Colorado Supreme Court. At the end of that term, he returned to his law practice in Delta. He was also in the Colorado Army National Guard, notably during the 1962 Cuban Missile Crisis and, between 1968 and 1979 served as its Commander, retiring with the rank of Brigadier General.
Eight weeks past his 90th birthday, Felix L. Sparks died in Colorado from complications due to pneumonia.