After several years organizing the Chicago Law Library, Mayer practiced with Adolf Kraus.

[1] His parents had immigrated from Bavaria three years earlier and moved to Chicago, Illinois when Mayer was young.

He edited two collections of manuscripts from David Rorer, one on judicial & execution sales and the other on interstate or private international law.

[2] The Supreme Court of Illinois admitted Mayer to the bar upon reaching age 21; he then left the library to practice with Kraus & Brackett.

[2] At the time of his death, he was the senior partner of Mayer, Meyer, Austrian & Platt and had offices in Chicago and New York City.

[2] In 1895, he defended the group in the Supreme Court of Illinois in Ritchie v. People, which outlawed the eight-hour workday limit for women.

Mayer was able to convince a judge to move the case to Peoria, Illinois and successfully had the charges against theater manager Will Davis dismissed.

In 1908, he defended the Mattoon City Railway Streetcar Company after an accident resulted in eighteen deaths.

[4] Late in his life he worked with distillers to fight the Eighteenth Amendment to the United States Constitution.

[5] He oversaw the sale of the Detroit Times to Arthur Brisbane on behalf of William Randolph Hearst in 1921.