Brien McMahon was an American lawyer and politician who served in the United States Senate from 1945 to 1952. McMahon was a major figure in the establishment of the Atomic Energy Commission, through his authorship of the Atomic Energy Act of 1946.

The Atomic Energy Act of 1946 determined how the United States would control and manage the nuclear technology it had jointly developed with its World War II allies, the United Kingdom and Canada. Most significantly, the Act ruled that nuclear weapon development and nuclear power management would be under civilian, rather than military control, and established the United States Atomic Energy Commission for this purpose.