After WWII was over, Cox returned to the law firm Ropes, Gray with the intention of spending his professional career there. Instead, he lasted five weeks. Dean Landis of the Harvard Law School offered to hire Cox as a probationary teacher in the fall of 1945. Cox accepted, despite the substantial cut in salary he would take, but on the condition that he would not have to teach corporations or property. Landis agreed; his expectation was that Cox should become a nationally recognized expert in labor law. In addition to labor law, Cox started out teaching torts. Later he would also teach unfair competition, agency and administrative law. He was made a permanent professor during the 1946–47 academic year, a time when the law school greatly increased enrollment in the post-war boom.
