Mabel Walker Willebrandt (May 23, 1889 – April 6, 1963), popularly known to her contemporaries as the First Lady of Law, was an American lawyer who served as the United States Assistant Attorney General from 1921 to 1929, handling cases concerning violations of the Volstead Act, federal taxation, and the Bureau of Federal Prisons during the Prohibition era.

In February 1910, she married Arthur Willebrandt, the principal of the school where she was teaching, and they moved to Phoenix, where he recuperated from tuberculosis while she finished college and supported them on a teacher's salary.

[2] During her last semester of law school, Willebrandt began doing pro bono work in the police courts while still teaching full-time.

During World War I, Willebrandt served as head of the Legal Advisory Board for conscription cases in Los Angeles.

In 1921, at age 32, her law school professor and mentor Frank Doherty, as well as Senator Hiram Johnson and all the judges in southern California, recommended her for the post of Assistant Attorney General in the Warren G. Harding administration.

Despite the unpopularity of the law among both the general population and within the government, the underfunding of the Prohibition Bureau, and widespread bribery of enforcement agents, Willebrandt focused on reviewing prosecutions for violations of the Volstead Act, rating the work of U.S.

Willebrandt's actions earned her criticism among American attorneys after she dismissed several prosecutors who were hostile towards the prosecution of Volstead Act-related cases.

In addition, she submitted 278 cases of certiorari to the Supreme Court regarding the defense, clarification, and enforcement of the Prohibition Amendment and the Volstead Act.

Some of her tactics were criticized by Democratic candidate Al Smith, a "wet", particularly when she addressed a gathering of Methodist ministers in Ohio and urged them to tell their congregations to vote for Hoover, supposedly disregarding the established separation of church and state, although it was pointed out that that separation only applies to the use of state power.

[5] She also represented California based Fruit Industries who made Vine-Glo, a grape concentrate product that she had previously ruled legal as assistant attorney general despite it carrying a warning telling people how to make wine from it.

She defended Louis B. Mayer before the IRS and represented celebrities such as Jean Harlow, Clark Gable, and Jeanette MacDonald.

[5] She also got her pilot's license and promoted air travel with Amelia Earhart, a fellow member of the Aeronautical Chamber of Commerce.