Educated in Nairobi, Scotland and the United States, including at the San Francisco Conservatory of Music, Middlebrook worked at a number of different jobs, from portering and window cleaning to piano teaching and typesetting. A prolific writer and publisher of poetry, fiction, criticism, religious and social commentary, music and drama, including radio plays, he ran the Chamber Theatre of Adelaide in the 1970s - 1980s. He also produced sound recordings, A Swag of 15 Australian Songs (1988) and Shakespeare's Sonnets (published between 1980 and 1987). In the 1990s Middlebrook republished many of his earlier works.
Some typescript copies of his radio plays are held in the Battye Library, Western Australia.
