Rachael is a two-time Olivier nominee English stage, film and television actress.  She played Nancy Astley in the BBC drama Tipping the Velvet, and Millie in the ITV series The Bletchley Circle.

Rachael is the daughter of actress Diana Rigg and theatre producer Archibald Stirling.  Rachael attended Wycombe Abbey School and earned a BA in art history from Edinburgh University, where she performed with the Edinburgh University Theatre Company.  Rachael can speak Russian and is experienced in horse riding and jumping.

In terms of film, Rachael's first screen appearance was in the 1998 British comedy film Still Crazy.  Other film appearances include Maybe Baby, Redemption Road (2001), Complicity (with her Tipping the Velvet co-star Keeley Hawes), Another Life (with Vanity Fair actress Natasha Little), The Triumph of Love (with Mira Sorvino), as Mary Jones in Salmon Fishing in the Yemen and as Anna in Snow White and the Huntsman.

Rachael's first break in television was in the 2000 NBC miniseries In the Beginning, which was adapted from Genesis.  Stirling played the young Rebeccah, with her mother, Diana Rigg, as the older Rebeccah.  Her next notable role was Nan Astley in the 2002 BBC drama series Tipping the Velvet.  In 2011, Stirling starred in the BBC Four adaptation of D.H. Lawrence's Women in Love as Ursula Brangwen.  She portrayed Millie in both series of the ITV mystery drama The Bletchley Circle in 2012 and 2014.

Rachael appeared in a 2013 episode of Doctor Who titled "The Crimson Horror" alongside Rigg, Matt Smith and Jenna-Louise Coleman.  The episode had been specially written for Stirling and her mother by Mark Gatiss (marking the very first appearance of the two actresses together professionally) and was aired 4 May 2013 as part of Series 7.

In 2014, Stirling portrayed Kate Wilkinson in the Cold War spy thriller television series The Game, and appeared in the BBC Four comedy drama Detectorists as Becky, initially girlfriend, then wife, of Andy (played by Mackenzie Crook).  In 2015, Stirling played the part of Arabella Yount, the spendthrift wife of a banker, in the three-part BBCs series Capital based on John Lanchester's novel of the same name.

As well as film and TV Rachael is an established stage actor.  Rachael made her first major appearance on stage in 1996 as Desdemona in the National Youth Theatre revival of Othello at the Arts Theatre opposite Chiwetel Ejiofor in the title role.  A year later, again at the Arts Theatre with the NYT, she played Olive in the female version of The Odd Couple; while in 1998, portraying Kate in Dancing at Lughnasa for NYT at the Arts, she gave what The Stage reviewer described as "a performance of exceptional promise and authority”.  Rachael next appeared in diverse roles in plays such as Dusty Hughes' Helpless (Donmar Warehouse, 2000); A Woman of No Importance (Theatre Royal Haymarket, 2003); Anna in the Tropics (Hampstead Theatre, 2004); and Tamburlaine (Bristol Old Vic and Barbican, 2005), and she following her mother's footsteps as Lionheart's daughter in the National Theatre stage version of Theatre of Blood (2005).  In 2006, for the Peter Hall Company at the Theatre Royal, Bath, Rachael played Helena in Peter Gill's revival of Look Back in Anger, while in 2007 at Wilton's Music Hall in London, she starred as Yelena in David Mamet's version of Uncle Vanya, and as Katharina in The Taming of the Shrew.

Rachael starred onstage in The Priory directed by Jeremy Herrin at the Royal Court Theatre in 2009.  Her role as Rebecca earned her a nomination for Laurence Olivier Award for Best Performance in a Supporting Role.  In 2010 she appeared as Helena in Peter Hall's production of A Midsummer Night's Dream at the Rose Theatre, Kingston.  Rachael starred as Lady Chiltern in a 2010 production of An Ideal Husband at the Vaudeville Theatre, for which she received her second nomination for a Laurence Olivier Award.  From February to April 2012, she appeared as Sylvia alongside Mark Gatiss, Tobias Menzies, and Nancy Carroll in The Recruiting Officer, the acclaimed production at the Donmar Warehouse directed by newly appointed artistic director Josie Rourke.