His father was principal clerk- formerly secretary to the High Commissioner of India- in the India Office; of Irish birth, his family later settled at Hanwell, in the London Borough of Ealing.

When Montgomery was two years old, his family moved round the corner to "Domus", a "big house in a rural setting" that was built according to his father's instructions.

[1][2] He was educated at Merchant Taylors' School and graduated from St John's College, Oxford, in 1943, with a BA in modern languages, having for two years been its organ scholar[3] and choirmaster.

[5] He first became established under his own name as a composer of vocal and choral music, including An Oxford Requiem (1951), but later turned to film work, writing the scores for many British comedies of the 1950s.

Montgomery wrote both the screenplay and score of Raising the Wind (1961), and his other film scores included The Kidnappers (1953), Raising a Riot (1955), Eyewitness (1956), The Truth About Women (1957), The Surgeon's Knife (1957), Please Turn Over (1959), Too Young to Love (1959), Watch Your Stern (1960), No Kidding (1960), Twice Round the Daffodils (1962) and The Brides of Fu Manchu (1966).

Montgomery wrote detective novels and two collections of short stories under the pseudonym Edmund Crispin (taken from a character in Michael Innes's Hamlet, Revenge!).

[8] The whodunit novels have complex plots and fantastic, somewhat unbelievable solutions, including examples of the locked room mystery.

[14] The Requiem was followed by his final major work for chorus, the secular Venus' Praise (1952), a setting of seven sixteenth and seventeenth century English poems.

Both remained unfinished, and Amis complained that Montgomery was too busy "writing filthy film scores and stinking stories for the popular press".

[18] Philip Lane calls Montgomery "a composer of talent who was perhaps side-tracked, and, not helped by increasing alcoholism, unable to fulfil his full potential.

By now, the composer character, Broderick Thouless, is writing "difficult" film music and light concert works rather than the other way round (as it was with Napier in Frequent Hearses).

Otherwise he enjoyed a quiet life (enlivened by music, reading, church-going and bridge) in Totnes, Devon, where he resisted all attempts to develop or exploit the district, and visited London as little as possible.

A previously unpublished novella, featuring Gervase Fen, "The Hours of Darkness," has been included in the 2019 edition of the annual anthology, Bodies from the Library.