He was professor at Harvard Law School and senior administrator of the Marshall Plan from 1948 to 1951.
After the war, in 1948, he was appointed Deputy Chairman of the Commission for European Recovery, later known as the Marshall Plan, under Averell Harriman.
After overseeing the distribution of $12 billion in aid funds for post-war Europe for nearly two years and coordinating among 18 participating countries, he had acquired such a reputation that he continued to be responsible for international projects.
At Harvard Law School he established the program in International Legal Studies, which he headed 1954 to 1974.
[4] After his retirement from the Henry L. Stimson Professorship (1954–1978) at Harvard, he became a Distinguished Professor of Law at Suffolk University from 1978 until his death in 1995.