Career
She is best known for her role as Sarah-Louise Platt in the ITV soap Coronation Street from 1999 to 2007 and 2015 onwards and her role as Bex Fisher in the BBC school drama Waterloo Road from 2010 to 2011. Born in Rusholme, Manchester, England, O'Brien left Trinity C.E. High School with nine GCSEs. She starred in the drama Children's Ward in 1997, The Cops in 1998 and Clocking Off in 2000, playing the on-screen half sister of actor Jack P. Shepherd who later became her on-screen brother David Platt in Coronation Street.
At the age of sixteen, she joined Coronation Street in October 1999, taking over the role of Sarah-Louise Platt from actress Lynsay King (she was three years older than her character). O'Brien revealed in the British press in April 2007 that she would be leaving Coronation Street before the end of the year. Her first role after leaving Coronation Street was in the 2007 pantomime at Manchester Opera House, where she played the title character of Cinderella.
Her first television role post-Coronation Street was in the ITV police television drama Blue Murder, filmed whilst four months pregnant, in which she played a character called Amy Kirkland. O'Brien expressed interest in doing televised dramas and theatre work, although after becoming pregnant, she decided to put her career on hold. In 2010, O'Brien starred in the sixth series of the BBC school drama Waterloo Road as Bex Fisher, the eldest daughter of the new headmistress Karen Fisher.
In 2010, she also appeared in The Secret Diaries of Miss Anne Lister, in which she played the character of Miss Browne, a role which required her first on-screen lesbian kiss. Later in 2010, she appeared as a character in new television drama The Accused written by Jimmy McGovern, as well as starring in the 2010 series of Strictly Come Dancing. She was eliminated in the 5th week of the competition after failing to impress the viewers with her Argentine Tango.
She fell into the bottom two alongside Felicity Kendal who was saved thanks to the public vote. In 2010, she also appeared in an advert for Homepride Sauces "Tasty Tip". From 4 December 2010 to 3 January 2011, she played Snow White in Manchester Opera House's 2010/11 pantomime.
Between 14 January and 13 February 2011, she participated in the 2011 Strictly Come Dancing Live Tour. In October 2014, O'Brien announced that she will be reprising her role of Sarah-Louise Platt in Coronation Street in early 2015. The character returned on an episode broadcast on 30 March 2015.