Born in 1870 in Hobart, Australia, Marie Louise Hamilton Mack was the daughter of the Rev. Hans Hamilton Mack, and his wife Jemima James, both of whom immigrated to Australia from Ireland. Mack was one of seven children, and her sister Amy Eleanor Mack was also to become a writer. She was educated at Sydney Girls' High School, where she met Ethel Turner, with whom she would become lifelong friends.
Mack worked briefly as a governess, before becoming a journalist for the Bulletin, contributing a column called "A Woman's Letter." She married barrister John Percy Creed in 1896, and then moved to England in 1901, where she continued her work as a journalist and author. Mack published her first and only collection of poetry, Dreams in Flower, that same year. She subsequently spent some time in Italy, where she edited The Italian Gazette in Florence, from 1904-07. John Percy Creed died in 1914, and Mack became the first female war correspondent in Belgium that same year, reporting on the German occupation, and publishing A Woman's Experiences in the Great War in 1915. She returned to Australia in 1916, working as a lecturer and journalist, and marrying Allen Illingworth Leyland in 1924. She died in 1935.