Sarah Miles was born in the small town of Ingatestone, Essex, in south-east England.She first attended Roedean but at the age of 15 she enrolled at RADA, the Royal Academy of Dramatic Art. Shortly after her completion at the Royal Academy of Dramatic Art, Miles debuted in 1962 as Shirley Taylor in Term of Trial (1962), co-starring with Laurence Olivier, with whom she had a brief affair. The following year, Miles became a well-reputed actress of British New Wave with her roles in Joseph Losey's The Servant (1963) and in Michelangelo Antonioni's Blowup (1966).

After acting in a variety of plays from 1966 to 1969, Miles was cast as Rosy Ryan, the daughter of Tom Ryan in David Lean's 1970 film, Ryan's Daughter. Her performance earned a nomination for the Academy Award for Best Actress.

Although she has denied it, Miles is known for her frequent use of profanity. A November 1971 Cosmopolitan profile was subtitled "She uses words that would make a construction worker blush, but from her they sound refined". A profile in Women's Wear was titled "The Lady with the Truckdriver's Mouth".

Miles is a practitioner of urine therapy. Citing Gandhi, who was an adherent of it, she has followed the tradition for thirty years, maintaining that it has kept her healthy and vigorous.

In 1973, while filming The Man Who Loved Cat Dancing, her manager and associate David Whiting died under mysterious circumstances. During that same time, Miles was reported to be having an affair with Burt Reynolds, with whom she co-starred in the film.

Since 1973, Miles has gone through periods of semi-retirement, only to appear in a film or a TV program. She most recently appeared in Well at the Trafalgar Studios and the Apollo Theatre opposite Natalie Casey.

Miles was married twice to the British playwright Robert Bolt, 1967–1975 and 1988–1995. He wrote and directed the film Lady Caroline Lamb, in which Miles played the eponymous heroine.

Her brother is film director, producer and screenwriter Christopher Miles.

Sarah Miles has written the following books:

• A Right Royal Bastard, ISBN 0-330-33142-6
• Beautiful Mourning, ISBN 0-7528-0140-6
• Bolt from the Blue, ISBN 0-7538-0229-5
• Serves Me Right, ISBN 0-333-60141-6