Mayne was born in
Brisbane,
Colony of New South Wales in 1858. The area would become part of the Colony of Queensland in 1859. Mary Emelia Mayne was the second youngest of five children of Irish parents,
Patrick Mayne, a butcher and grazier, and his wife Mary McIntosh Mayne. She attended
All Hallows' School, a Catholic girls' school in Brisbane, until 1877. Thereafter she oversaw and hostessed many functions at
Moorlands, the family home at
Auchenflower. She and her siblings all inherited real estate, giving them independent means. Neither she nor her siblings would marry. ==James O'Neil Mayne==