She graduated from high school in 1911, earned her bachelor's degree in 1916 and her master's degree in 1927.
She published travel writing and short stories as well as biographies of prominent Finnish women, such as Sophie Mannerheim (1948), Ottilia Stenbäck (1950), Alexandra Gripenberg (1959) and Maila Talvio (2 volumes, 1963–1965).
She also wrote memoirs in three volumes (1966–1969).
In 1979, she published a collection of essays titled Fredrikan Suomi about Fredrika Runeberg and the other women who belonged to the circle around Johan Ludvig Runeberg.Tuulio is counted among Finland's most influential twentieth century literary translators.
She translated from Swedish (the collected works of Fredrika Runeberg), English (Charlotte Brontë, Louisa May Alcott) and the Romance languages (Dante Alighieri's La Vita Nova).In 1957, she received an award from the Finnish Cultural Foundation.
In 1960, she was awarded an honorary doctorate by the University of Helsinki.
In 1985, she received the State translation prize.She married linguist Oiva Tuulio in 1917; they had three sons.
Her brother was the conductor Toivo Haapanen.
She is buried in the Hietaniemi Cemetery in Helsinki.