Aronson worked at several publications prior to founding the National Guardian. He worked on the staffs of the Boston Evening Transcript, the New York Herald Tribune, the New York Post and The New York Times from 1946-48.

Aronson founded the National Guardian in 1949 with John T. McManus and Cedric Belfrage. It continued publishing until 1992.

Aronson also worked as a professor at Hunter College of the City University of New York. In 1981 he was invited to Mainland China to teach newswriting by the Chinese Academy of Social Sciences. Aronson was the first American to be invited to teach such classes since the Communists pushed the Nationalists off the mainland. In China he found that the content and style were what the Maoist government wanted to change about Chinese journalism, not the purpose.The James Aronson Award for Social Justice Journalism is named for him.