Lionel Casson was one of two sons in a Brooklyn Jewish family; his father owned a lumberyard. His original name was Lionel Cohen. He attended New York University for all his studies, earning a bachelor's degree in 1934, a master's in 1936 and his Ph.D. in 1939. He joined the faculty as an instructor and then served as an officer in the United States Navy during World War II. After the war, Prof. Casson returned to NYU, where he served as a professor of classics from 1961 to 1979. In 1952, he received a Guggenheim Fellowship that allowed him to examine the site of important ancient harbors on the coast of the Mediterranean. He wrote 23 books on maritime history and classic literature, using as his sources various ancient materials ranging from Demosthenes's speeches to ship cargo manifests and archeological studies of ancient shipwrecks and the contents of the amphorae they carried.
The New York Times said in his obituary that Prof. Casson "melded his mastery of classical literature with the findings of underwater archaeology in scholarly but accessible books about the history of ancient seafaring, from the primitive dory to the vast armadas of the Roman Empire."