Aside from being a radio personality and talk show host, Greene was also a community activist, joining the United Planning Organization and founding the Ralph Waldo Greene Community Centre and Efforts for Ex-Convicts. This organization remains devoted to helping former prisoners succeed in legitimate ways and to advocate prison reform. He rallied against poverty and racism on his shows and on the streets, participating in demonstrations during the height of his popularity. Following the assassination of Dr. Martin Luther King Jr. in April 1968, and during the subsequent riots that erupted throughout the United States, Greene made statements on air that were credited with helping quell the riots in Washington, D.C.