Dellinger was highly educated, he studied at Yale University, Oxford University, as well as the Yale and Union Divinity Seminary schools.  Dellinger was an ardent pacifist, and believed that pacifism could be used as a tool for change rather than simply a defense for one's beliefs.  Dellinger thought that "particapatory democracy and civil disobedience were to be at the heart of all activity".  Practicing what he preached, Dellinger was active in anti-war activity at a very early stage. 

Dellinger was one of the keynote speakers at the 1965 Berkeley teach in, designed to inform students about the war America was increasingly becoming involved in.  By 1966 Dellinger was the co-chair of the Spring Mobilization to End the War in Vietnam.  He became very controversial when he visited Hanoi in 1966.  While his visit actually helped free some American POW's, he set a precedent for other Americans to visit Northern Vietnam in protest.  His participation in the debacle that occured at the Democratic National Convention in 1968 earned him a place as one of the "Chicago Seven".