An archaeologist and university lecturer, Quinnell specialised in the archaeology of South West Britain.
Born in Oxfordshire in 1944, Quinnell took a first-class undergraduate degree in Archaeology at the University of Wales in Cardiff and married Trevor Miles while still an undergraduate in 1967. They divorced in 1975 and Quinell went on to marry Norman Quinnell, an archaeological surveyor, in 1980.
She first came to the South West in 1968. She became a staff tutor at the University of Exeter in 1970. A practical archaeologist, she directed excavations for the Inspectorate of Ancient Monuments across the UK and was particularly interested in rescue archaeology.
She became the President of the Devon Archaeological Society in 1987-9 and of the Cornwall Archaeological Society in 2004-7. She as also the Editor for the journal Cornish Archaeology from 1975-81.