Charlotte Endymion Porter was born in Towanda, Pennsylvania as Helen Charlotte Porter. As a young woman, she discarded her first name and adopted "Endymion" from a poem by John Keats. She graduated from Wells College in Aurora, New York, in 1875 and studied at the Sorbonne in Paris.
At age 26, she became the editor of Shakespeariana, a journal published by the Shakespeare Society in New York. She met Helen Archibald Clarke, who would become her lifelong partner, when she accepted Clarke's article about music in Shakespeare. After they met, the two women did almost all of their literary work together for many years. In 1889, they founded Poet Lore, a new monthly magazine devoted to Shakespeare, Browning, and comparative literature, and wrote much of the content themselves. They introduced American readers to many European authors in translation, including Henrik Ibsen, August Strindberg, Gabriele D’Annunzio, Selma Lagerlöf, Maxim Gorky, Maurice Maeterlinck, and Rabindranath Tagore. In 1903, they sold Poet Lore, though they continued to edit the magazine, in order to work on other projects. Poet Lore is still published today, making it the oldest continuously published poetry magazine in the USA. Porter and Clarke published a collection of short stories they had translated called Clever Tales (1897); a 12-volume complete edition of Browning’s works in 1898; a 6-volume edition of Elizabeth Barrett Browning’s works in 1900; and the 12-volume Pembroke edition of Shakespeare in 1912. Porter herself dramatized Browning's Return of the Druses in 1902 and put together a 40-volume work entitled First Folio Edition of Shakespeare (1903–1913). She also published Lips of Music (1919), a poetry collection.