Horter was born in Germantown, Philadelphia. He was a self-taught artist who engraved stock certificates as a teenager. A superb draftsman and technician, Horter was first employed as a commercial artist working for N.W. Ayer, the largest advertising agency in Philadelphia and third largest in the country. Throughout his career, Horter produced a tremendous body of work consisting of drawings, lithographs, and etchings that depict large cities such as Philadelphia and New York. In his etching of Naples, Italy, he captures the activity a busy market scene where a merchant sells goods from a cart. A clothing line covered in laundry is suspended behind a woman sitting on a bench.
Horter played an important role in introducing modern art to Philadelphia, not only as an artist and teacher, but also as a collector. Throughout the 1930s, he taught at the Philadelphia Museum School (now the University of the Arts) and Temple University’s Tyler School of Art, exposing students to the formal innovations of the cubist artists. His works are in numerous public collections, including the Philadelphia Museum of Art; the Pennsylvania Academy of the Fine Arts; the Metropolitan Museum of Art; the Library of Congress, Washington, D.C.; and the Free Library of Philadelphia. His collection, which was exhibited in 1999 at the Philadelphia Museum of Art in their exhibition, Mad for Modernism: Earl Horter and His Collection, included African sculptures and Native American artifacts as well as works by seminal modern artists Pablo Picasso, Georges Braque, Marcel Duchamp, and Constantin Brancusi.