Horowitz lives in North London with his wife Jill Green. He married her in Hong Kong on 15 April 1988. Green produces "Foyle's War". Horowitz writes this series for ITV. They have two sons. They are Nicholas Mark Horowitz (born 1989) and Cassian James Horowitz (born 1991). The family have a dog named Lucky, that has been run over 3 times. Horowitz says that his family has a lot to do with his success in writing. This is because he says they help him with ideas and research. Horowitz is a patron of child protection charity Kidscape.