Initially a hurdler, Craig developed into a sprinter at the University of Michigan. In 1910, he won the IC4A 220 y championship, repeating this the following year.
In 1912, Craig qualified for the Olympic team and went to Sweden, where he reached the final of the 100 m. A big favourite was his compatriot Don Lippincott, who had set a World Record of 10,6 in the heats. After no less than seven false starts, Craig won the race in 10,8 - Lippincott only finished third. Craig fought out another battle with Lippincott in the 200 m, edging him to win the 200 m title. Craig was not a part of the American 4 x 100 m relay team, which was disqualified and didn't medal.
Immediately after the Olympics, Ralph Craig retired from the sport. In 1948, he made a return to the Olympics as an alternate on the US yachting team. Although he did not actually compete, Craig (59) carried the American flag at the opening ceremonies in London.