Freund was an influential constitutional law scholar and professor.

After serving as a law clerk for Supreme Court justice Louis Brandeis, Freund worked for the Roosevelt Administration’s Justice Department, arguing for a more flexible interpretation of the Constitution in economic and social matters.

In 1939, Freund began his influential and lengthy career at Harvard Law School, where he developed and taught a complex understanding of the judicial system and the Supreme Court’s crucial role.

In 1992, then Harvard Law School Dean James Vorenberg eulogized Freund as "the dominant figure of his time in the field of constitutional law."