Thomas Gray was born in Kearny, New Jersey, in 1944. He attended Emerson School and Kearny High School, during which time he joined the Naval Reserve at the age of seventeen.
Following high school graduation, he started to attend University College at Rutgers-Newark and then switched to Rutgers College, where he pursued an English major and joined the fraternity Chi Psi. While at Rutgers, joined the Marine Corps and went to Officer Candidates School (OCS) at Quantico between his junior and senior years. Upon graduating in the Rutgers College Class of 1966, Gray was commissioned as a second lieutenant in the Marine Corps. He completed artillery school at Fort Sill in Oklahoma and then the Naval Gunfire Air Spotters Course in Coronado, California.
In 1967-1968, he served in Vietnam, first as a forward observer in an artillery battalion, the Third Battalion, 11th Marines, and then as an intelligence analyst in the First Marine Division Headquarters. After returning to the U.S. in early 1968, he was assigned to Camp Pendleton as a part of the Fifth Marine Expeditionary Force. Following discharge from active duty, Gray stayed in the Reserves and went to law school at the University of San Diego on the GI Bill. He worked for thirty-three years as a prosecutor in the office of the District Attorney of Los Angeles County.