Conversation so far:
What was M. John Harrison's first novel?
The Committed Men is M. John Harrison's first novel.
Did M. John Harrison write in any other genre before writing Science fiction?
In M. John Harrison's early years, his hobbies included writing pastiches of H. H. Munro.
How popular were M. John Harrison's first stories?
M. John Harrison's first short story was published during 1966 by Kyril Bonfiglioli at Science Fantasy magazine, on the strength of which he relocated to London.
Who influenced M. John Harrison as a writer?
In an interview with Zone magazine, M. John Harrison says I liked anything bizarre from about four years old. I started on Dan Dare and worked up to the Absurdists.

Question: Who published his first novel?
Self-contained rewrite: Who published M. John Harrison's first novel?