Mathias was born in Tulare, California. He attended Tulare Union High School, where he was a classmate and long-time friend of Sim Iness, the 1952 Olympic discus gold medalist. While at Tulare Union in early 1948, Mathias took up the decathlon at the suggestion of his track coach, Virgil Jackson. During the summer following his high school graduation, he qualified for the United States Olympic team for the 1948 Summer Olympics held in London.
In the Olympics, Mathias’s naïveté about the decathlon was exposed. He was unaware of the rules in the shot put and nearly fouled out of the event. He almost failed in the high jump but was able to recover. Mathias overcame his difficulties and with superior pole vault and javelin scores was able to push past Ignace Heinrich to win the Olympic gold medal. At age 17, he became the youngest gold medalist in a track and field event.
Mathias continued to fare well in decathlons in the four years between the London games and the 1952 Summer Olympics in Helsinki. In 1948, Mathias won the James E. Sullivan Award as the nation’s top amateur athlete, but because his scholastic record in high school did not match his athletic achievement, he spent a year at The Kiski School, a well-respected all-boys boarding school in Saltsburg, Pennsylvania. He then entered Stanford University in 1949, played college football for two years, and was a member of the Phi Gamma Delta fraternity. Mathias set his first decathlon world record in 1950 and led Stanford to a Rose Bowl appearance in 1952, the first nationally televised college football game.
After graduating from Stanford in 1953 with a BA in Education, Mathias spent two and a half years in the U.S. Marine Corps. He was promoted to the rank of captain and was honorably discharged.
In Helsinki in 1952, Mathias established himself as one of the world’s greatest all-around athletes. He won the decathlon by the astounding margin of 912 points, which established a new world record, and he became the first person to successfully defend an Olympic decathlon title. He returned to the United States as a national hero. His 7,887 point total at the Helsinki Olympics remained the school record at Stanford for 63 years until it was broken in 2015 by a freshman, Harrison Williams. In 1952, he was the first person to compete in an Olympics and a Rose Bowl the same year.
After the 1952 Olympics, Mathias retired from athletic competition. He later became the first director of the United States Olympic Training Center, a post he held from 1977 to 1983.
He and his wife Melba can be seen on the 29th April 1954 edition of You Bet Your Life. During the discussion, he mentions a forthcoming film in which the couple played themselves, called The Bob Mathias Story. He also starred in a number of mostly cameo-type roles in a variety of movies and TV shows throughout the 1950s. In the 1959–1960 television season, Mathias played Frank Dugan, with costars Keenan Wynn as Kodiak and Chet Allen as Slats, in the TV series The Troubleshooters, which focused 26 episodes on events at construction sites. In 1960, he also appeared playing an athletic Theseus in an Italian “peplum,” or sword-and-sandal, film: Minotaur, the Wild Beast of Crete.