Eleanor Daniels was born on 28 December 1886 in Llanarthney, Carmarthenshire, the daughter of David Daniels, a hay merchant and publican, and his wife Margaret. She was brought up at the Fountain Inn on Thomas Street in Llanelli, in a Welsh-speaking family; Welsh was her first language, and she began winning eisteddfod recitation prizes as a child. She won first prize in three National Eisteddfodau, at Swansea in 1907, London in 1909 and Carmarthen in 1911, when she became a member of the Gorsedd of the National Eisteddfod under the bardic name Ellyw.
In 1913 she joined the movement for a National Welsh Drama, appearing in Little Miss Llewelyn, The Joneses at the Strand Theatre and The Mark of Cain. In 1914 she toured the United States with the Welsh Players, alongside fellow Llanelli actor Gareth Hughes, to perform J. O. Francis's prize-winning play Change at the Booth Theatre in New York. Her reception was strong enough that she chose to remain in America for the rest of her life.
She worked for a number of years with the Broadway producers Comstock and Gest, appearing in Heart of the Heather, Kitty McKay, Loyalty and, opposite Richard Bennett, Zach, as well as in the musical comedies Kitty Darling, Lassies and La La Lucille. She also starred with Florence Reed in Ashes and with Jeanne Eagels in Rain, and in Juno and the Paycock she played Maisie Madigan. Between 1914 and the mid-1920s she appeared in a number of silent films, most notably If Winter Comes (1923) with Percy Marmont and Bebe Daniels. In 1930, alongside Gareth Hughes, she received Gorsedd Honours for her contribution to drama.
In later life Eleanor Daniels worked as a vocal coach in New York, and in 1951 took an office job with an American diabetes organisation, working there until she was 87. She died at the age of 107 on 18 March 1994 at a house in Darien, Connecticut. In 2011, a blue plaque was unveiled by her niece at the house in Llanelli where she grew up.