MacInnes served in the British Intelligence Corps during the Second World War, and worked in occupied Germany after the European armistice. These experiences resulted in the writing of his first novel, To the Victors the Spoils. Soon after his return to England, he worked for BBC Radio until he could earn a living from his writing.

He was the author of a number of books depicting London youth and black immigrant culture during the 1950s, in particular City of Spades (1957), Absolute Beginners (1959) and Mr Love & Justice (1960), known collectively as the "London trilogy". Many of his books were set in the Notting Hill area of London, then a poor and racially mixed area, home to many new immigrants and which suffered a race riot during 1958. Openly bisexual, he wrote on subjects including urban squalor, racial issues, bisexuality, drugs, anarchy, and "decadence".
Mr Love & Justice concerns two characters, Frank Love and Edward Justice, during late 1950s London. Mr Love is a novice ponce (pimp); Mr Justice is a police officer newly transferred to the plain-clothes division of the Vice Squad. Gradually their lives intermesh.