Lee was born on March 29, 1891, in Petersburg, Virginia, as a son of Leonard Rogers Gerow and Annie Eloise Saunders.

Subsequently, he spent some time as assistant commandant of Columbia Military Academy in Tennessee, before he was commissioned a second lieutenant in the Regular Army on November 30, 1916.

Gerow was promoted to the rank of major on September 26, 1918, and transferred to the Camp Sherman, Ohio, where he assumed command of 3rd Battalion of the 379th Infantry Regiment.

His new task was to take charge of the payment of the Bonus granted by Congress to the all honourably discharged soldiers who had served between April 6, 1917, and November 11, 1918, in the World War.

Gerow was subsequently sent overseas, where he was assigned to the American Expeditionary Forces, where he was appointed a commanding officer of the Visitors Bureau, stationed in Koblenz, Germany.