Moritz Heim was probably the first lawyer in Minnesota to specialize in international law. Before the First World War, he represented the consulates of many European countries and handled litigation that established basic principles of consulate law. He maintained offices in Chicago and Pittsburgh to handle the volume of consul work (he may be one of the first Minnesota lawyers to have branches in other states).
He died on July 13, 1932, at age sixty-seven. In memorial services for the Ramsey County Bar Association the following year, he was recalled for his representation of Czechoslovakia and Poland in negotiating treaties with the United States:
"After the conclusion of the World War and the formation of new European states, Mr. Heim became quite active in the practice of international law. He was the author of the treaty negotiated between United States and then new Republic of Czecho-Slovakia, which he represented, the draft of which treaty was written by him in the City of St. Paul; and he was also largely responsible for the drafting of the treaty of between United States and Poland, finally ratified by both of these countries. He was well versed in international law as well as domestic law, and in fact his work on the treaties referred to brought him considerable prominence in this connection. He was also known for his knowledge of foreign law, and on different occasions he was called upon in Court to testify as to the law of various European countries."