William Guarnere was born in Philadelphia, Pennsylvania on 28 April 1923 to Italian parents Joseph and Augusta Guarnere. He attended Citizens Military Training Camp for three summers, which took 4 years to complete. Guarnere enlisted in the U.S. Army on 31 August 1942 and was assigned to Easy Company, 2nd Battalion, 506th Parachute Infantry Regiment, 101st Airborne Division, in the Mortar Squad of 2nd Platoon.