Hornig was born in Milwaukee, Wisconsin, the son of Chester Arthur Hornig and Emma Knuth. He attended Milwaukee Country Day School, then earned his undergraduate degree in chemistry from Harvard University. He was awarded his Ph.D. from Harvard University in 1943, at the age of 23, with a dissertation on An Investigation of the Shock Wave Produced by an Explosion in Air.[1] On July 17, 1943 he was married to scientist Lilli Hornig.