His father was of English (paternal) and Irish (maternal) heritage and his mother of English and Scottish ancestry.
Eldred Gregory Peck was born on April 5, 1916, in La Jolla, San Diego, California. He was the son of Gregory Pearl Peck, a New York-born chemist and pharmacist, and his Missouri-born wife Bernice Mary "Bunny" (née Ayres). She converted to her husband's religion, Roman Catholicism. Through his Irish-born paternal grandmother Catherine Ashe, Peck was related to Thomas Ashe, who participated in the Easter Rising less than three weeks after Peck's birth and died while being force-fed during his hunger strike in 1917.
Peck's parents divorced when Gregory was five and he was brought up by his maternal grandmother, who took him to the movies every week.