Frank Daniel Gilroy was born on October 13, 1925, to Bettina Vasti and Frank B. Gilroy in the Bronx, New York. He was educated in the Bronx and graduated from De Witt Clinton High School in 1943, after which he joined the U.S. Army. During World War II, he served for two and a half years with the eighty-ninth infantry division, including eighteen months in Europe. After leaving the army, he received his bachelor of arts degree (magna cum laude) from Dartmouth College in 1950. With a grant from Dartmouth, he spent the following year at Yale Drama School.

Gilroy soon began writing for television. During the 1950s, he wrote for Playhouse 90 (CBS), Studio One (CBS), U.S. Steel Hour (ABC), Omnibus (CBS), Kraft Theatre (NBC), and Lux Video Theatre (NBC). Gilroy's first staged play was Who'll Save the Plowboy?, performed at New York's Phoenix Theatre in 1962. It won...