Millicent Sylvia Armstrong (1 May 1888 – 18 November 1973) was an Australian playwright and farmer who wrote primarily about the experiences of country life in early 20th century Australia.

She worked as an orderley in World War I in France, and was awarded the Croix de Guerre for bravery in rescuing wounded soldiers while under fire.

She matriculated in French and Latin in 1905 and entered Sydney University to study arts, following her two older sisters, Ina Beatrice and Helen Daphne.

Millicent's sister, Helen, with whom she would collaborate on plays and a novel, graduated with first class honours in French, English and German in 1902.

In 1914 Armstrong travelled to England to pursue a writing career but became involved in World War I work almost immediately.

Armstrong's first post-war play was Fire, which won third prize in the Sydney Daily Telegraph playwriting competition in 1923.

A sinisterly dramatic play about two sisters who live in the Australian bush, one of whom dies of fright after encountering a vicious man from her past, is described as 'plunder[ing] the 'frontier mentality' which usually saw women scripted as saviours rather than victims of intolerably discriminatory situations.