[9] She received her secondary education at Sherborne School for Girls in Dorset, and then attended Trinity College Dublin.
Leslie remained at the university, where she was academically successful, winning a gold medal in 1922 and gaining her D. Litt in 1943 for work on Felicia Hemans.
[10][11] Leslie wrote poetry and novels under two pen names, those of Jean Herbert and Temple Lane.
[10][12] She was a member of Dublin's Women Writers' Club, which had been founded by Blanaid Salkeld along with Dorothy Macardle, Elizabeth Bowen, Helen Waddell, Maura Laverty, Winifred Letts, Sybil le Brocquy, Patricia Lynch, Rosamond Jacob, Hanna Sheehy Skeffington, Nora Connolly O'Brien, Christine Longford, Ethel Davidson (President of the Club in 1937) and Teresa Deevy.
As Davidson put it, their aim was sharpening "the wits, and improving the standard of criticism, as well as encouraging the writers".