Oates was born in Pike County, Alabama, to William and Sarah (Sellers) Oates, a poor farming family. At the age of 17, he believed that he had killed a man in a violent brawl and left home for Florida. Oates became a drifter, settling in Texas for a couple of years before returning to Alabama at the urging of his younger brother John, who had been dispatched by the family to locate him. He studied law and passed the bar examination, and then opened a practice in Abbeville.