He was a direct descendant of Lieutenant William Ennis who served in the Continental Army during the American Revolution and was an original member of the Rhode Island Society of the Cincinnati.

Ennis married Frances Cassel Dwyer (1903–1994) on April 27, 1927, shortly after his graduation from West Point.

In Italy he served as the assistant commander of the IV Corps Artillery in support of Free French forces.

[2] He was awarded the Legion of Merit and the Bronze Star Medal with two oak leaf clusters for his service during World War II.

Ennis was promoted to lieutenant general on July 30, 1960, and was assigned as commanding officer of the Weapon Systems Evaluation Group in Washington, D. C. He retired from the Army on August 31, 1962, after 36 years of active service.