Referred to by the media as both "Bill" and "Willie" (actually Hartack detested being called "Willie" because of his dislike for fellow jockey Willie Shoemaker) during his racing career, Hartack grew up on his widowed father's farm in the Blacklick Township area of Cambria County, Pennsylvania. Small in stature, at age 17 he stood 5 ft. 4 in. (1.63 m) and weighed 111 lb (50 kg), a size that enabled him to pursue a career as a jockey in Thoroughbred horse racing. By his third season of racing, Hartack was the United States' leading jockey, going on to win that honor on three more occasions. He and Eddie Arcaro are the only two jockeys to ever win the Kentucky Derby five times. As well, Hartack won the Preakness Stakes three times and the Belmont Stakes once. He rode Tim Tam to victory in the 1958 Florida Derby but two weeks before the Kentucky Derby, Hartack broke a leg and had to give up his ride on Tim Tam, who won the race.
During his riding career between 1953 and 1974 in the United States, Hartack rode 4,272 winners in 21,535 mounts. From 1978 to 1980 he raced in Hong Kong, then retired in 1981. Hartack led the nation in races won four times, and was the first rider to have purse earnings of $3 million in a season.
After he retired as a jockey, Hartack worked off-and-on for the rest of his life as a steward for many racetracks.
Hartack made the cover of Sports Illustrated magazine in 1956 and again in 1964, plus the cover of Time Magazine in 1958. He was inducted into the National Museum of Racing and Hall of Fame in 1959 at the early age of 27.
Winners ridden in Triple Crown Classic races :
1956 : Fabius 1964 : Northern Dancer 1969 : Majestic Prince
1960 : Celtic Ash
On November 26 2007, Hartack was found dead in a cabin at a camp near the town of Freer, Texas, in southern Texas, where he went each winter to hunt. The cabin was checked because he had not been seen by his friends since the previous day. He died from natural causes due to heart disease, according to the chief medical examiner in Webb County.
The camp where Hartack was found is the property of the Thoroughbred owner Greg Goodman, a friend and client of Stidham's. Stidham's father George was Hartack’s agent at the end of the jockey's career.