Stephens, nicknamed the "Fulton Flash" after her birthplace Fulton, Missouri, was a strong athlete in sprint events - she never lost a race in her entire career - but also in weight events like the shot put and discus throw, and she won national titles in both categories of events.
Aged only 18, Stephens was sent out to the 1936 Summer Olympics. There, she won the 100 m final, beating reigning champion and reigning world record holder Stanisława Walasiewicz of Poland (at autopsy, it was discovered that Walsh had both male and female sex organs). Her time of 11.5 s was below the world record, but was not recognised because a strong tailwind was present at the time of the race. Next, Stephens anchored the American 4 x 100 m relay team that won the Olympic title after the leading German team dropped its baton.
Stephens retired from athletics shortly after the Games and played some professional baseball and softball. She attended William Woods University, Fulton High School, and Middle River School in Fulton. From 1938 to 1952, she was the owner and manager of her own semi-professional basketball team. She was employed for many years in the Research Division of the U.S. Aeronautical Chart and Information Service (later, a part of the Defense Mapping Agency) in St. Louis, Missouri.
At the 1936 Olympics it was suggested that Stephens and her 100 metres rival Stella Walsh, who had both X0 and XY chromosomes, were in fact male. The Olympics committee performed a physical check on Stephens and concluded that she was a woman.