At the age of seven she began modelling for knitting patterns, and showed an early flair for performing. This resulted in her attending the Sylvia Young Theatre School. As a student, she appeared in the chorus of Les Misérables with fellow Sylvia Young student Melanie Blatt, and then as Eponine - the role paid her school fees; the Anthony Newley directed production of Stop the World - I Want to Get Off, and A Midsummer Night's Dream with the Royal Shakespeare Company.
Success was not forthcoming, and she turned to being a glamour model (which included one topless shoot for a lads mag). Van Outen has retained her distinct looks, being voted both Rear of the Year in 1999, and top of a poll to find the most desired "bikini body" in a 2007 poll of readers of Grazia magazine.
She took a break from presenting the show towards the end of 1998 but returned in 2000 for a further year-long stint in an attempt to boost the ratings, which had tailed off following her departure. When the show closed down, van Outen gave Vaughan a present of a set of AMG wheels for his Mercedes Benz CLK - commented on as "very Essex Girl" by Jeremy Clarkson when the pair appeared on the BBC's Top Gear programme.
Van Outen then returned to television. The revival of her on screen relationship with Vaughan failed in 2004 in the BBC's Saturday night family revival show "Passport to Paradise," but she returned again in mid-2005 to co-presented ITV's This Morning with Richard Bacon.
Van Outen had been set to present How Do You Solve A Problem Like Maria? in 2006 for the BBC, a programme searching for a girl to play the role of Maria in The Sound of Music, but pulled out in favour of seeking fame in America and was replaced by Irish comedian Graham Norton.. She subsequently presented NBC's Grease: You're the One that I Want!
After her commitments ended on the show she began re-establishing her television career in the UK. In November 2006, she hosted Sky1's The Race - set at Silverstone Circuit - in which a celebrity Girls Team headed by David Coulthard raced against a celebrity Boys Team headed by Eddie Irvine. In December 2006, she hosted the National Lottery Christmas special, and in January 2007 hosted one show of The Friday Night Project. She also guested on The Charlotte Church Show, and was one of the judges at the Miss World pageant in Warsaw, Poland.
In 2007, she joined the panel for BBC One's follow up to How Do You Solve A Problem Like Maria?, Any Dream Will Do! which was casting Joseph in Joseph and the Amazing Technicolor Dreamcoat. After viewers on 9 June 2007 voted Lee Mead as the winner of Any Dream Will Do! - to play the role of Joseph in a revival at London's Adelphi Theatre of Joseph and the Amazing Technicolor Dreamcoat van Outen said: "From the very beginning right through to the very end, Lee has been the most consistent out of all the contestants. He has the ability to make even really popular songs his own and he has his own unique style of performing. The next time he lands a role as a leading man, can he put me forward to be the leading lady?"
Denise will present a new Saturday night entertainment series for ITV1, alongside Ben Shephard, called Who Dares Sings. Challenging 100 members of the studio audience to hit the right notes in the largest karaoke competition on TV.
Van Outen has also appeared in film, initially as Maureen in the crime comedy Love, Honour and Obey. She also had a cameo tease as red head Alex, a slut, in the low-key Tube Tales in one of the four separate short films, based on the London Underground. Other directors included Ewan McGregor, Jude Law and Jarvis Cocker; while her part in "Horny" was directed by Lost In Space director Stephen Hopkins. Most recently, Van Outen has played a small role in the Romantic Comedy Are You Ready For Love?
She first played Roxie Hart on the stage in the hit musical Chicago at the Adelphi Theatre in the West End in April 2001. Her run proved a hit with theatre-goers, selling out for the entire 20 weeks. Unknown in the United States, she reprised her role on Broadway for five weeks in the spring of 2002, before returning to the show's London version in late April 2002. Late the same year, Van Outen appeared as one of many special guest stars in a performance of The Play What I Wrote'' once again in London's West End.
In 2003, she returned to the London stage at the Gielgud Theatre in Andrew Lloyd Webber's one-woman show Tell Me On A Sunday, which he reworked for her. She was a huge success and the show ran for nearly a year before embarking on a 10-month UK tour in 2004. She then joined the cast of the established ITV sentimental drama Where the Heart Is as one of the lead characters, playing single mother Kim Blakeney, but stayed for only one series.
Van Outen played Maureen in the 2007 London revival of RENT until December 22, when the role was taken over by former EastEnders actress Jessie Wallace. Van Outen was forced to cancel some performances due to a throat infection.
However, on July 29, 2008 it was reported that she had decided to quit the show after only half of her contract had been completed, owing to the effect that early morning starts were having on her health.
From 2003 she dated lap dance club owner Richard Traviss, but split up with him in May 2005 due to his infidelity, moving out of the Marylebone home they shared and back into her own garden flat in Hampstead, North London. After appearing on Channel 4's "The Friday Night Project" and describing her first real kiss with fellow "Sylvia Young" student James Lance, he got in touch and they shared a short romance in 2007. As of November 2007, she has been dating Any Dream Will Do winner, Lee Mead, who is eight years younger than her. She has a house in Hove.
Van Outen has lent her support to design limited edition T-shirts or vests for the 'Little Tee Campaign' for Breast Cancer Care which donates money for breast cancer research.