In 2003, Billie was selected to play Alison in the BBC's adaptation of The Miller's Tale. The show was a success and less than a year later she had landed parts in several films and BBC 2’s Bella and the Boys, a drama focusing on three residents of a children's care home.
However, success really peaked for Billie when she was chosen to play the part of Rose Tyler in the BBC resurrection of Doctor Who. The show was critically and popularly acclaimed, immediately becoming one of the most acclaimed shows of all time. Billie went on to receive several awards including, 'Most Popular Actress', 'Best Actress' and 'Breakthrough British Talent' at numerous different ceremonies. Two years and two series later, Billie decided it was time to move on, resulting in a huge public outcry, subsequently seeing the final episode with Billie as the most watched episode in BBC’s history. Since leaving, Billie was voted as the single most popular Doctor Who companion of all time and has returned frequently to the show, much to public delight. Celebrations in 2013 for Doctor Who's 50th Anniversary propelled the show to become an even bigger hit when Billie returned, along with many other former cast members, in what is now one of the most successful live events in cinema history, after selling out worldwide in more than 1,500 cinemas. The episode on television, which now holds the Guinness World Record for the largest ever simulcast of a TV Drama, was watched in 94 countries across six continents with the UK alone producing nearly 11 million viewers, whilst over in America it was the BBC's most watched show of all time.
From 2005 to 2007 Billie starred in many successful adaptations including BBC's Shakespeare Re-Told where she played Hero in Much Ado About Nothing, female detective Sally Lockheart in The Ruby in the Smoke and The Shadow in the North and Fanny Price in ITV's acclaimed Mansfield Park.
The years of 2007 to 2011 saw Billie play the role of a high-class escort in ITV's highly controversial but highly popular, Secret Diary of a Call Girl, based on the blog by Belle de Jour. The show was a huge ratings success and went on to become one of the channel's biggest hits. Though some critics had mixed opinions on the subject, it nevertheless went on to four massively popular and successful series, earning more award recognition. The final episode of series four saw, yet another public outcry, as emotions and disappointment ran high in reaction to the end of the show.
In 2010 Billie starred alongside Sue Johnston in BBC 1's A Passionate Woman, a two-parter written and directed by Kay Mellor, which saw her yet more acclaim. On-screen improvisation was something Billie had not tried until 2012’s True love, playing the part of another controversial role, a teacher falling in love with one of her female students. The series was highly anticipated and a hit with fans and ratings, alongside critics commending Billie's performance.
2014 was a big year for Billie with another lead role in a play at the National Theatre, but on both sides of the Atlantic, she was starring in Showtime's Penny Dreadful. A huge ratings and critical success, the series returned for three series.. She also played the lead role in Foxtrot for Sky Arts, which saw glowing reviews for her performance, becoming another acclaimed title as part of the 'Playhouse Presents...' series.