Horn met his future wife Jill Sinclair, a former mathematics teacher and business partner, in 1977. They married in 1980 and became business partners. They have four children: two sons, Aaron and Will (formerly known as Rebecca), and two daughters, Gabriella and Alexandra, the latter of whom has worked as a trainee solicitor. Aaron (known in the industry as "Aaron Audio"), like his father, is a musician and producer. He was in the band Sam and the Womp and frequently DJs around London. Both Aaron and Ally Horn are co-directors of Sarm Studios. , Horn has three grandsons. He is not Jewish, but has attended synagogue with his children, who were raised in his wife's faith. In a 2019 interview, he said that he "believes in more than anything else".