Drawing on psychologists such as Sigmund Freud and Jean Piaget, Frank proposed that judicial decisions were motivated primarily by the influence of psychological factors on the individual judge.

In 1942, he published If Men Were Angels, a defense of the ambitious New Deal programs, and governmental regulation in general, expressing views that he developed while serving in the SEC.

Beginning in 1946, Frank also began teaching a regular course on legal fact-finding at Yale Law School which "emphasized the parts that human fallibility and partisanship play in the trial court processes".

[2] In 1949, he published his most significant work after Law and the Modern Mind, this being Courts on Trial, which stressed the uncertainties and fallibility of the judicial process.

[2] Frank was initially offered the position of solicitor of the United States Department of Agriculture, but this appointment was blocked by Postmaster General James A. Farley, who favored another candidate for the job.

(Some of these lawyers were members of the Ware Group spy ring run by Whittaker Chambers, namely: Alger Hiss, Lee Pressman, Nathan Witt, and John Abt).

[2] Roosevelt agreed, and Frank served as an SEC commissioner from December 1937 until 1941, and was elevated to Chairman from 1939 to 1941, when Douglas was appointed to the United States Supreme Court.

[2] In 1938, Frank also published a book titled Save America First, which had been written during his return to private practice and advocating against American involvement in the stirring conflict in Europe.

[10] Frank was nominated by President Franklin D. Roosevelt on February 13, 1941, to a seat on the United States Court of Appeals for the Second Circuit vacated by Judge Robert P.

[10] In addition to his reputation for expertise on civil liberties matters, he was also considered to be "an outstanding judge in the fields of procedure, finance, [and] criminal law".

[2] For a time, he was sharply and vocally at odds with a colleague on the bench, Charles Edward Clark, "over a whole range of common law precepts".

[4] In the 1956 case United States v. Roth,[26] Frank wrote a concurring opinion to the decision, which affirmed the obscenity conviction of a criminal defendant.

In a lengthy appendix to his concurring opinion, Frank "drew on a host of historical, literary, and social science studies to point to the dangers and contradiction of all forms of government censorship of ideas and images".

The concurrence has been asserted to be one of Frank's most important opinions, and one which set the stage for the direction the Supreme Court would take on such issues beginning in the 1960s.

At least one legal commentator has written that "[f]ew jurisprudential writers have aroused such prolonged public controversy as Jerome Frank".