L
- Ring Lardner Jr., Academy Award winning screenwriter of M*A*S*H, member of the Hollywood Ten
- Frank Lavin, current Undersecretary for International Trade of the United States Department of Commerce (graduated 1975)
- Alan J. Leavitt, light harness horse breeder, author. (graduated 1963)
- George Ayres Leavitt, early New York publisher (graduated 1840)
- Gary Lee, journalist, travel writer (graduated 1974)
- Nate Lee, writer, senior editor of Newcity in Chicago (graduated 1974)
- Jack Lemmon, actor (graduated 1943)
- I. Lewis "Scooter" Libby, former lawyer, government official, policy advisor, novelist. (graduated 1968)
- Gordon Lish, editor, author, teacher. (graduated 1952)
- Seth Lloyd, physicist and researcher in quantum information theory (graduated 1978).
- Dave Longstreth, founding member of American rock band The Dirty Projectors
- Alfred Lee Loomis, father of ultrasonics (graduated 1905)
- Phillips Lord, American radio program writer, creator, producer and narrator (deceased 1975)
Read more about this topic: List Of Phillips Academy Alumni