Miranda Raison was born in Burnham Thorpe, Norfolk. Her mother, Caroline Raison read the news for Anglia Television and her father, Nick Raison is a jazz pianist . She is the great-niece of Thomas William Edward Coke, 5th Earl of Leicester, the granddaughter of Max Raison and the niece of Timothy Raison. Her parents divorced when she was five years old and from the age of nine she attended several boarding schools, including Gresham's School, Felixstowe College and Stowe School.

Raison trained at the Webber Douglas Academy of Dramatic Art.

She has voiced several video game characters including Cassandra Pentaghast in the Dragon Age series.

Raison has also voice-acted in several Big Finish Doctor Who audios including "The Davros Mission" and "The Wreck of the Titan".