Muriel Jefferis was the second youngest of ten children born to the Reverend James Jefferis, LLD (1933-1917), congregational minister, lecturer and journalist, and his second wife, Marian (1847-1930). She was born while the family was visiting England, but her early years were spent in Sydney. James Jefferis, one of the founders of the University of Adelaide, believed in a good education for his children, and with her sister Nance, Muriel attended boarding school at Milton Mount.
In 1894 the family returned to North Adelaide, where James Jefferis had previously worked from 1959-1877, and Muriel ("Mu") Jefferis attended Dryburgh House School. Her father bought the Fountain Inn at Encounter Bay for a holiday house, and renamed it "Yelki". Between the ages of 16 and 19 Muriel Jefferis wrote the poems which were later printed in her book In Sun and Shade. She was also a skilled painter, and a photograph of her painting of "Yelki" is included in M. A. Denton's biography, Joanna Priest: Her Place in Adelaide's Dance History (1993).
In 1906 Muriel married the Reverend Fred Priest, a congregational minister, who had trained at Hackney College, London, and after a time as a social worker in York, had come to Australia to a pastorate at Hamley Bridge in 1905. Their first two children were born at Hamley Bridge. In 1909 they moved to Henley Beach, where Joanna (1910-1997), who was to become well-known as a teacher of ballet and ballroom dancing, was born.
In 1911 the family moved from Henley Beach to Marrickville, New South Wales, where they lived until Priest accepted a position in North Perth, Western Australia in 1921. In 1925 Priest died suddenly of a heart attack. Muriel Jefferis and the children remained in the manse until they had built a house of their own. Jefferis continued to live in Perth, although after her daughter Joanna settled in Adelaide she made frequent visits to South Australia. The novelist Barbara Jefferis (qv) is the daughter of Muriel Jefferis' younger brother, Tarlton.