Born in New York City, she was the daughter of cellist Gregory Aller (né Grisha Altschuler), a Jewish emigre from the Russian Empire. Her mother Fannie had studied piano at the Warsaw Conservatory. Eleanor attended Juilliard where she studied with Felix Salmond.
Eleanor Aller became principal cellist in the Warner Bros. Studio Orchestra in 1939, of which her brother, pianist Victor Aller, later became orchestra manager and in which their father also played for a time. The same year she met and married Felix Slatkin. Shortly after their marriage, the couple founded the Hollywood String Quartet. Aller also continued working as a Hollywood studio musician. She performed the Cello Concerto by Erich Korngold for the soundtrack of the movie Deception (1946 film) starring Bette Davis and Paul Henreid. Eleanor also performed the concert premiere of the Concerto with the Los Angeles Philharmonic in 1946.
Aller continued to work as principal cellist for movie soundtracks, including a solo specially written for her by composer/conductor John Williams for the soundtrack to the 1977 Steven Spielberg movie Close Encounters of the Third Kind.
She was the first woman to hold a principal chair in a Hollywood studio orchestra 
- "Fred Zlotkin Reminisces: about growing up in the Slatkin household with parents Felix and Eleanor Slatkin and brother Leonard Slatkin". London: The Felix Slatkin Website. September 9, 2003. Retrieved 2008-01-05.[permanent dead link] "My grandfather Gregory Aller's name, prior to his coming to America at the turn of the century, was Grisha Altschuler. He changed the named to "Aller" because (or so I was told) there were so many Altschulers -- indeed, it is a very common name. The Altschuler side of the family is really rife with musicians. Grisha's uncle, Modest Altschuler, was a cellist (making me 4th generation) and he had quite a career. Among other things, he did the St. Petersburg premiere of Tchaikowsky's "Souvenir de Florence" Sextet. When he came to America he formed the Russian Symphony Orchestra (early 1900s). "
- Brad Hill, Classical (American Popular Music series) NY, 2006.