Daniela Denby-Ashe was born in London in 1978, and she has a brother two years her junior. Denby-Ashe is of exclusively Polish descent. Her father, Mirosław Pszkit, was born in Poland and came to the United Kingdom aged 12.

Denby-Ashe's mother was born in the UK and raised in France, but had Polish parents. Because of this, Denby-Ashe is fluent in French and Polish, as well as English.

Daniela Denby-Ashe was first seen on television in an advert for KP Skips, which then led her to her big break when, in 1995, she got the role of Sarah Hills in EastEnders. She played this character until 1999.

The following year, she got the role of Janey Harper in a new BBC sitcom called My Family. Denby-Ashe took a break from My Family for the fourth series in 2003, but returned to this role in 2004.

In 2004, she took the lead female role of Margaret Hale in the BBC drama adaptation of Elizabeth Gaskell's North & South, and in 2006 played Mary in the Torchwood episode Greeks Bearing Gifts.

Her other television roles include Is Harry on the Boat?, Office Gossip, Rescue Me and The Afternoon Play. In 2005, she appeared in a Radio 4 comedy called Ring Around the Bath.

Denby-Ashe has also performed at the Yvonne Arnaud Theatre and Criterion Theatre, London in The Countess and in Motortown at the Royal Court Jerwood Theatre.