As a fiction writer, Herdman's main publications have been Descent (1968), A Truth Lover (1973), Memoirs of my Aunt Minnie / Clapperton (1974), Pagan's Pilgrimage (1978), Stories Short and Tall (1979), Imelda and Other Stories (1993), Ghostwriting (1995), Four Tales (2000), The Sinister Cabaret (2001), and My Wife's Lovers (2007).
His fictions have a metaphysical flavour and a preoccupation with psychological duality, as well as strong elements of the surreal, the satirical and the grotesque.