Series 1, Correspondence, 1915-1955, is arranged chronologically and primarily documents the scheduling (and not content) of Hays's speaking engagements and housekeeping details related to his writings. There are occasional letters to editors and other memoranda regarding issues of substance. The most significant segment of this series are those files identified as relating to Hays's involvment with the ACLU.

Series 2, Case Files, 1921-1956, is arranged alphabetically by case name and includes correspondence, court papers, legal briefs, and other items related to particular court cases in which Hays was a participant. The bulk of this series consists of material regarding the numerous legal motions filed in many high-profile cases involving Hays such as labor disputes in the coal mining districts of Pennsylvania and West Virginia (1922-1935), including the Anthracite Coal Strike of 1922 and right to strike cases taken against Jersey City, NJ mayor Frank "Boss" Hague; John Strachey's deportation case; the Emerson Jennings vs. Commonwealth of Pennsylvania conspiracy case; the Jehovah's Witnesses and the right not to salute the American flag; the case of Stanley E. Faithful vs. the Daily Mirror and other newspapers on charges of libel concerning the circumstances of his daughter's death; and cases relating to communism and sedition in the 1940s. Hays work in various organizations is also represented in this series, including his service on the Mayor's Commission on Conditions in Harlem (formed after police killed a Harlem man under suspicious conditions) and the Committee for Fair Play to Puerto Rico (organized to investigate civil liberties after the Ponce massacre of 1937 in which police killed fifty demonstrating civilians). The general and miscellaneous portions of this series contain printed materials such as briefs, motions, appeals, and petitions for various cases.

Series 3, Speeches, 1923-1954, is arranged alphabetically by speech and contains the text of various speeches that Hays delivered. Subject matter of speeches is as wide-ranging as the cases he worked on, but are colored with personal anecdotes, human history, and current events. Topics include prejudice, strike breaking, the Reichstag Fire, war and civil liberties, fascism, the Dies Committee, politics and political races, and the status of working women.