Fletcher was born in Derby, Derbyshire. She played Nancy in Fairly Secret Army, and has appeared in other popular British television shows such as Coronation Street as Angela Hawthorne, Inspector Morse, Agatha Christie's Poirot, Within These Walls, Midsomer Murders and Heartbeat. In 1971 she appeared in No One Was Saved at the Royal Court Theatre schools scheme. Her first film was Roman Polanski's Macbeth.
In the BBC adaptation of House of Cards and its sequels To Play the King and The Final Cut, Fletcher played Elizabeth Urquhart, wife of the murderous Chief Whip of the Conservative Party and later Prime Minister Francis Urquhart (played by Ian Richardson).
Fletcher is the mother of anthropologist, Dr Jamie F. Lawson, whose father is the actor Denis Lawson.
- Diane Fletcher at the Internet Movie Database
- "Dublin Theatre Festival biography of Diane Fletcher". Dublin Theatre Festival. Archived from the original on 17 June 2007. Retrieved 24 October 2015.