From 1889 to 1895 he was instructor in Greek at Barnard College and Columbia University. From 1895 to 1898 he served as associate professor in Greek and Latin at Bryn Mawr College, before returning to Barnard in 1898 just as it was about to become part of Columbia University.[5] He was appointed professor of classical philology in 1899. In 1890 he was appointed a member of the American Philological Association and served as vice-president from 1902 until his untimely death in 1905.[6] He edited Euripides' Alcestis (1895); Sophocles' Œdipus Tyrannus (1900); and Euripides' Medea (1904). His numerous contributions to learned periodicals were collected in The Classical Papers of Mortimer Lamson Earle, with a Memoir (New York, 1912). He died on September 26, 1905, in New York from typhoid fever contracted whilst in Sicily.[7][8]
After his death, his students and friends gave his library to his alma mater, Columbia University.