After graduation, he joined the faculty and took a one-year leave to clerk for Justice Harlan F. Stone of the US Supreme Court.
This included leading the litigation for Korematsu v. U.S., the case challenging the Japanese Internment during World War II.
It was also around this time that Wechsler authored a number of casebooks that changed ideas about criminal law and the federal courts.
In 1963, Wechsler's proposed official draft of the Model Penal Code was approved, bringing to a close a decade-long project at the American Law Institute.
The ALI's Principles of Corporate Governance and the current Restatement of Foreign Relations Law of the United States were also conceived, initiated, and developed under his direction.