At the age of sixteen, she joined Coronation Street in October 1999, taking over the role of Sarah Platt from actress Lynsay King.

[3] Her first role after leaving Coronation Street was in the 2007 pantomime at Manchester Opera House, where she played the title character of Cinderella.

O'Brien expressed interest in doing televised dramas and theatre work,[4] although after becoming pregnant, she decided to put her career on hold.

[7] Later in 2010, she appeared as a character in the new television drama Accused, written by Jimmy McGovern,[7] as well as starring in the 2010 series of Strictly Come Dancing.

From 4 December 2010 to 3 January 2011, O'Brien played the title character of Snow White in Manchester Opera House's 2010/2011 pantomime.

[10] In October 2014, O'Brien announced that she would be reprising her role of Sarah Platt in Coronation Street in early 2015.