Leslie Rees was educated at Subiaco Primary School, Perth Modern College and the University of Western Australia (1924-1929). While at the University of Western Australia, he edited the student magazine, Black Swan. He became a journalist for The Westralian after graduating with an Arts degree and, in 1929, received a scholarship to University College in London. While in London he married fellow West Australian, Coralie Clarke Rees (q.v.). Rees was appointed Senior Dramatic Critic for the weekly newspaper, The Era, in 1931 and he held this position until 1935.
Rees returned to Australia in 1936, becoming the Australian Broadcasting Commission's first federal drama editor and remaining in this position with the ABC until 1966. With Doris Fitton and Rex Rienits (qq.v.), Rees founded the Playwrights Advisory Board in 1956 and was its chairman for 25 years. He was President of PEN (Sydney) for some years.
As a writer, he is perhaps best known as a prolific author of children's stories but he has also written travel books, plays and an autobiography, Hold Fast to Your Dreams (1982). Rees's major critical work is the two volume Making of Australian Drama. Volume one covers the period from the 1830s to the late 1960s and volume two extends the study from 1970 to 1985. Rees also wrote numerous articles and critical essays, other histories of Australian drama and edited collections of plays. Rees's work has been published in many countries and languages.