Lewis Hershey was born on September 12, 1893, in Steuben County, Indiana. As a youngster, Lewis attended the local public schools. After his high school graduation, Lewis trained as a teacher at Tri-State College, now known as Trine University. After earning a bachelor of science in 1912 and a bachelor of arts in 1914, he taught at local elementary schools and served as a school principal in Flint, Indiana.
In 1911, Lewis enlisted in the Indiana National Guard. Almost immediately, his guard unit was called to active duty on the Mexican border, where they served until December, 1916. That year he was commissioned as a second lieutenant. His unit was again called to federal service during World War I, when Lewis was deployed to France as part of the American Expeditionary Force. After the war ended, Lewis continued his education at both the Command and General Staff College and the Army War College, graduating in 1933. Then Lewis taught military science at Ohio State University.
Lewis retired from the Army as a four-star general in 1973, at the age of 79. Suffering from heart failure, he passed away in Angola, Indiana in 1977, and was buried at Arlington National Cemetery.