Born in Rusholme, Manchester, O`Brien left Trinity Church of England High School with nine GCSEs.[citation needed] She starred in the drama Children`s Ward in 1997, The Cops in 1998 and Clocking Off in 2000, playing the on-screen sister of actor Jack P. Shepherd who later became her on-screen brother David in Coronation Street. She joined Coronation Street on 31 October 1999, taking over the role of Sarah-Louise Platt from Lynsay King,at the age of sixteen.She was three years older than her character. Sarah`s pregnancy with baby Bethany won O`Brien Best Storyline at the British Soap Awards.[1] She has also won best newcomer at the National Television Awards.[1] O`Brien revealed in the British press on 4 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. O`Brien has expressed interest in doing televised dramas and theatre work.

O`Brien is the godmother of Emily Walton, who plays Bethany, her on-screen daughter. Since 2004, Tina has been in a relationship with Ryan Thomas who played her onscreen husband Jason Grimshaw, and in March 2008 it was revealed they are moving in together. On 5th April 2008, it was announced that Tina and Ryan were expecting their first child together. Their daughter, Scarlett Jacqueline Thomas was born on 26th October at 8:28am, weighing 7lb 1oz. Tina gave birth in Manchester General Hospital. She previously dated Bruno Langley, who played Todd Grimshaw in Coronation Street. O`Brien has twice been voted into the annual FHM Top 100 Sexiest Women in the World. In 2005 she was voted 28th. In 2006 she was voted 53rd. O`Brien is a patron of the charity Animals in Distress Sanctuary. In Coronation Street, her character hates her younger brother David Platt, played by Jack P. Shepherd, but in real life she and Shepherd are good friends.