Eclair was born to English parents in Kuala Lumpur, Malaya, where her father, Derek Hargreaves, a major in the British Army, had been posted in 1952.

She is said to have adopted the alternative surname Eclair (later her stage name) in her teens, when she was at a disco in Blackpool and pretended to be French.

"[7] In 1995, Eclair was the first woman to win the Perrier Award at the Edinburgh Fringe Festival for her show Prozac and Tantrums.

[10] Eclair returned to her birthplace of Kuala Lumpur (Malaysia) to explore the historical background of the Malayan Emergency in which her father had fought.

She confronted her father who confirmed that they were real and that collecting severed heads was a common practice by the British military in Malaya.

[17] She was a contestant in the fifteenth series of Taskmaster (aired March–June 2023), alongside comedians Frankie Boyle, Mae Martin, Kiell Smith-Bynoe and Ivo Graham.

[18] On 25 January 2014, Eclair took part in the second series of the ITV celebrity diving show Splash!, appearing in the fourth heat.

In January 2024, she was a contestant on Richard Osman's House of Games Until April 2008, Eclair hosted a weekend talk show on LBC 97.3.

Between 2014 and 2022, Eclair wrote seven series (36 episodes) of Little Lifetimes,[23] short monologues for female actors, broadcast on BBC Radio 4.

As well as Eclair herself, actors including Dame Harriet Walter, Haydn Gwynne, Monica Dolan, Vicki Pepperdine, Imelda Staunton, Anita Dobson and Ruth Sheen have been the monologist.