Prenger was educated at Elmslie Girls' School in Blackpool and Blackpool and The Fylde College before starting work in the area as an entertainer. She has performed extensively on the cabaret circuit in Northern England and particularly her hometown of Blackpool and Fylde coast where she has also worked as an agony aunt. In June 1998 she appeared in two different shows each night in two Blackpool theatres. First she had a solo spot in the Tiptoes Summer Spectacular at the resorts Opera House theatre before appearing 20 minute later in one of the principal roles in a Blackpool and The Fylde College production of the musical comedy, Hot Mikado at the Grand Theatre.

Her first appearance on television came in 1999 when she appeared on A Taste for Travel on Granada Television alongside her mother. In 2000 she took part in the Dale Winton show The Other Half on BBC1 in which she had to pretend to be the wife of boxer, Chris Eubank. Later that year she played the role of the good witch Hurricane in a non-skating role in Halloween Spectacular On Ice at Alton Towers in Staffordshire. In 2001 she spent eight months as one of four principals in a team of 19 entertainers aboard the Disney Wonder cruise ship.

Prenger won the second series of The Biggest Loser in 2006, starting the show a size 22 and weighing 115 kg (18st 2lbs). During the series, she lost over 51 kg (eight stone). Her final weight was 61 kg (9st 9 lbs) and she slimmed down to a size 10 before settling at a size 14/16. She won £25,000 for winning the series. In 2006 Jodie Prenger was also featured on Charlotte Coyle's Fat Beauty Contest on channel 4, where Coyle searched for plus sized models for a beauty pageant.

On 10 March 2009 Prenger appeared on The Paul O'Grady Show and spoke about her time on the Biggest Loser. On seeing a picture of herself after initially losing weight, she said that she believed she lost too much weight and became too thin at that time. She also commented that she believed all women should have curves, which she had also stated in a Daily Mail article on 16 February.

Prenger was the winner of I'd Do Anything, announced on 31 May 2008, giving her the opportunity to play Nancy in a West End revival of the British musical Oliver! at the Theatre Royal, Drury Lane.

Prenger attended auditions for the show in Manchester in January 2008, and made it through to the final 42 at "Nancy School" from where she was eventually chosen as one of the twelve finalists to perform in the live shows each week.

After her performance of "Chasing Pavements" in the first live show of the series, Prenger was installed as the joint favourite to win. Panelist John Barrowman said, "I love you to death, you connected with everyone and told the story – that's making a good Nancy!" Denise Van Outen said "Nancy needs to have a lot of life experience and I see that coming through in your performance. It was absolutely brilliant". Barry Humphries who had played Fagin in the original Lionel Bart stage production, said "You've got that toughness and also a tenderness. A beautiful performance and a fine actress." And head judge Andrew Lloyd Webber said that Jodie could "absolutely play this role."

In Week five Barry Humphries said that Prenger was "destined for the West End", and in Week Eight John Barrowman labelled Prenger his "perfect Nancy".

In the week leading up to the final in week ten, the Nancy finalists posed for publicity pictures recreating some of Madonna's iconic images. Prenger posed in a wedding dress to recreate the cover of the album Like a Virgin. She was also installed as the favourite to win the show. On 30 May, Andrew Lloyd Webber revealed that Theatrical producer Cameron Mackintosh, who will be producing the show in the West End, and who joined the panel in week nine, was concerned about her curvaceous figure saying, "Cameron thinks she is a bit too big and has more or less said so". However, Webber defended Prenger, saying that she had both the vocal talents and personality for the role, saying "Jodie could be anybody's idea of Nancy - I can see it absolutely. She has got a lovely voice and a super personality. She has experience as well."

In the Final on 31 May Prenger performed a total number of seven songs including her performance of "As Long as He Needs Me" after she was announced as winner. She also performed "I'd Do Anything" with all the Nancy and Oliver finalists; "Son of a Preacher Man"; "Getting To Know You" from the musical The King and I with Laurence ; "Maybe This Time" from the film Cabaret with Jessie Buckley and Samantha Barks as well as also singing "As Long as he Needs Me" and "I Have Nothing" from A Star Is Born before the final vote.