Mathias graduated high school, in the class of 1948. He earned the gold medals for the United States in the decathlon in the 1948 and 1952 Summer Olympic Games in London and Helsinki respectively.
In the 1952 Olympic Games, Mathias set a world record in the decathlon with 7,887 points. Mathias was the first person to successfully defend a decathlon title in the Olympic Games. Following that career accomplishment, he retired from athletics competitions.
Aside from being a world class athlete, Mathias was a U.S. Marine Corps officer, and a United States congressman that represented the northern San Joaquin Valley of the state of California. He served four terms in the U.S. House of Representatives from 1967 to 1975.
Two years later, in 1977, Mathias become the first director of the United States Olympic Training Center, a position which he held until 1983. He passed away on September 2, 2006, at the age of 75, after a long battle with cancer, but his athletic legacy will live on forever.