Julian William Mack (July 19, 1866 – September 5, 1943) was a United States Circuit Judge of the United States Commerce Court, the United States Court of Appeals for the Seventh Circuit, the United States Circuit Courts for the Seventh Circuit, the United States Court of Appeals for the Second Circuit and the United States Court of Appeals for the Sixth Circuit.

Mack was born on July 19, 1866, in San Francisco, California,[1] the son of William Jacob and Rebecca (Tandler) Mack.[2] His father, who came from Bavaria about 1849, was a Jewish merchant, engaged in business successively in Cincinnati, Ohio, Terre Haute, Indiana, San Francisco, California, and again in Cincinnati.[2] Mack received his early education in the public schools of Cincinnati,[2] then received a Bachelor of Laws in 1887 from Harvard Law School.[1] He graduated at the top of his class, and was selected as the class orator for graduation in 1887.[2] Encouraged by Harvard law professors, Mack and several of his classmates founded the Harvard Law Review.[2] He served as its first business manager and as a member of the editorial board.[2] He received a Parker Fellowship from Harvard University and attended the Humboldt University of Berlin and the University of Leipzig in the German Empire from 1887 to 1890.[1] He entered private practice in Chicago, Illinois from 1890 to 1895.[1] He was a Professor of Law for Northwestern University from 1895 to 1902.[1] He was a Professor of Law for the University of Chicago from 1902 to 1911.[1] He was a Judge of the Illinois Circuit Court for Cook County, Illinois from 1904 to 1905.[1] He was a Judge of the Illinois Appellate Court from 1905 to 1911