[1] Mack was an active participant in many of the social reform movements which emerged in Chicago and the nation during the 1890s and early twentieth century.

[2] Mack worked at Hull House and taught social workers at the Chicago School of Civics and Philanthropy, and later became President of the National Conference of Charities and Correction.

[2] He was an early supporter of the National Association for the Advancement of Colored People and the American Civil Liberties Union.

[1] He was confirmed by the United States Senate on January 31, 1911, and received his commission the same day.

[1] Mack was reassigned by operation of law to the United States Court of Appeals for the Sixth Circuit and the United States Court of Appeals for the Second Circuit on July 1, 1929, to a new joint seat authorized by 36 Stat.

[1] On June 30, 1930, Mack was reassigned by operation of law to serve on the Second Circuit only, pursuant to the provisions of 36 Stat.

[3] Mack was a member of the United States War Department Board of Inquiry on Conscientious Objectors from 1918 to 1919.