Horowitz was born in Stanmore, Middlesex, into a wealthy Jewish family, and in his early years lived an upper middle class lifestyle. As an overweight and unhappy child, Horowitz enjoyed reading books from his father's library. At the age of 8, Horowitz was sent to Orley Farm, a boarding preparatory school in Harrow, Middlesex. There, he entertained his peers by telling them the stories he had read.
Horowitz was appointed Officer of the Order of the British Empire (OBE) in the 2014 New Year Honours for services to literature.
- Judgement Day
- Dead Man's Eleven
- Strangler's Wood
- Death's Shadow
- Written in Blood
- The Killings at Badger's Drift (along with Caroline Graham