Born in Tokyo, the tenth and youngest child of Hugh Waddell, a Presbyterian minister and missionary who was lecturing in the Imperial University. She spent the first eleven years of her life in Japan before her family returned to Belfast.
Waddell was educated at Victoria College for Girls and Queen's University Belfast, where she studied under Professor Gregory Smith, graduating in 1911. She followed her BA with first class honours in English with a master's degree, and in 1919 enrolled in Somerville College, Oxford, to study for her doctorate. A travelling scholarship from Lady Margaret Hall in 1923 allowed her to conduct research in Paris.
She is best known for bringing to light the history of the medieval goliards in her 1927 book The Wandering Scholars, and translating their Latin poetry in the companion volume Medieval Latin Lyrics. A second anthology, More Latin Lyrics, was compiled in the 1940s but not published until after her death. Her other works range widely in subject matter. Her historical novel Peter Abelard was published in 1933 and was critically well received and became a bestseller.
She also wrote many articles for the Evening Standard, the Manchester Guardian and The Nation, and did lecturing and broadcasting.
Waddell received honorary degrees from Columbia, Belfast, Durham and St. Andrews and won the Benson Medal of the Royal Society of Literature.
A serious debilitating neurological disease put an end to her writing career in 1950. She died in London in 1965 and was buried in Magherally churchyard, County Down, Northern Ireland. A prize-winning biography of her by the Benedictine nun Dame Felicitas Corrigan was published in 1986.
