[1] Forrest was born near Yandilla, Queensland (now part of Toowoomba Region), the daughter of James Checkley Mills and his wife Margaret Nelson, née Haxell.

She became well known as a writer of verse following the publication of her first volume of poems, Alpha Centauri, which appeared in Melbourne in 1909.

Poems by M. Forrest, a collection of her verse contributions to Australian, English and American magazines, was published at Sydney in 1927.

[2] In addition to her work in book form, for the last 30 years of her life Forrest poured out a constant stream of verse and short stories for newspapers and magazines.

Forrest died of pneumonia on 18 March 1935 in Brisbane, after a long illness and only two days after her last poem, 'Waning Moon', appeared in the Australasian.