He completed his accounting degree after World War II, and joined a Pennsylvania law firm. When the Korean War began, he joined the Central Intelligence Agency. He became a guerilla warfare instructor at the CIA training facility known as "The Farm" (Camp Peary) at Williamsburg, Virginia. He was deputy chief of the CIA task force for operation PBSuccess which overthrew Jacobo Arbenz in 1954, the President of Guatemala. He was CIA station chief in Guatemala, Venezuela and Panama. Jacob Esterline's first child was a boy, who has his father's namesake.