Born David Mortlock on 27 August 1953, he grew up in Barking, Essex, UK, later moving to Basildon New Town, where he attended Barstable School.
After several years as a musician, he commenced a PhD study on soil erosion modeling at Brighton Polytechnic, under the supervision of geomorphologist John Boardman.
He is married to fellow musician and painter Joanna Davies; they live near Crickadarn, Powys.
Favis-Mortlock is also a musician; in 1978 he formed a Banbury-based folk group named after the nearby Rollright Stones, together with Adderbury morris dancer, the late Bryan Sheppard.
Subsequently, Favis-Mortlock played fiddle with guitarist Frank Underwood, and with the Brighton-based folk-punk band Tricks Upon Travellers.