She was educated at Westminster School and Lady Margaret Hall Oxford, receiving a congratulatory first in English in 1988. She was awarded a PhD at the University of East Anglia in 2007.

Miller worked as deputy literary editor of the Independent in the mid 1990s. Well-known for her seminal study in metabiography, The Bronte Myth (published by Jonathan Cape in the UK in 2001 and Knopf in the USA in 2003) she has also been a regular contributor to The Guardian, as a profile and comment writer, a reviewer for the Times Literary Supplement and the Economist and was one of the judges of the Man Booker Prize in 2009. She has been a trustee of the London Library and the Wordsworth Trust and is currently editorial director of Notting Hill Editions.

Miller is married to the tenor Ian Bostridge.