She was born Rebecca Jayne Atkinson, the only surviving child from her mother's first marriage to Paul Atkinson. Her parents divorced in 1978, and her mother remarried three times, to David Sowden, Steven Callard, and Jon McEwan. As a young actor, Rebecca was credited in early roles as Rebecca Sowden; she changed her stage name to Rebecca Callard following her mother's 1989 marriage to Steven Callard.

Callard married actor Gideon Turner in 2001 but they separated in 2016.

Callard appeared on stage as Juliet at the age of eighteen in Romeo and Juliet, directed by Judi Dench. She played Celia in the UK and US tour of a production of Shakespeare's As You Like It, Rosalind being played by Rebecca Hall. After a four-year break, she returned in 2009 with a production of another Shakespeare play Macbeth at the Royal Exchange Theatre, Manchester, and in a guest star role in an episode of the television series Robin Hood. In 2011 she played the part of Ruth Walsh in the drama soap Coronation Street.

In 2012 she played Ruth Pulis in the BBC crime drama series Blackout. In 2013 she played Sarah in The Accrington Pals at the Royal Exchange and appeared in the feature film Orthodox also starring Stephen Graham and Michael Smiley.

In 2015 Rebecca played Grace Wells in the BBC1 series Ordinary Lies. She also played a car mechanic, Toni, in the 2015 Christmas special and 2017 series 3 of the BBC4 comedy Detectorists.

In February 2016 she appeared in the BBC drama series Moving On. After appearing in the 2017 ITV drama series, Fearless, she claimed she was relieved not to have any scenes with its star, Michael Gambon, because she and her younger son, George, are such Harry Potter fans that she would have been tempted to "hound him with questions".