 Stewart was born in Sydney on 20 November 1858.Her father, Richard Stewart (originally Towsey)(c. 1826–1902), was an actor and singer who, in 1857, married Mrs. Guerin, née Theodosia Yates, a great-granddaughter of the famous actor and actress Richard Yates and Mary Ann Yates.Nellie's mother came to Australia in 1840 and took leading parts in opera.