Wiley, born in rural Southern Indiana, studied at Hanover College, apprenticed to a KY doctor, earned his MD degree from Indiana Medical College, and then earned his B.S. degree from Harvard. He took advanced training at the Imperial Health Office in Berlin, thus making him an expert in food adulteration practices. He taught at Purdue University and became Indiana State chemist. During these years he became a major foe of impure foods and patent medicines. In 1883 Wiley was called to Washington, D.C. to become chief chemist of the Department of Agriculture and it was from this position that he would lead the successful fight to gain passage of the 1906 Pure Food and Drug Act.