She will have to adopt and American accent to play the touch Roxie Hart in the musical, which won the 1998 Olivier Award for Outstanding Musical Production.
In her West End debut Van Outen will play Roxie, a chorus girl who has murdered her lover but manages to get acquitted with the help of a sleazy lawyer.
Van Outen, 26, attended the Sylvia Young Theatre School in London and appeared in productions such as Les Miserables from the age of 11, but this will be her first time treading the boards in ten years.
"People coming to see the show will hopefully see more than just TV's bubbly blonde and I hope it will open a few more doors for me," said Van Outen, who added she was very excited about getting back to theatre.
It adds to a dramatic week for Van Outen, which began on Monday with a narrow escape from court proceedings when she produced her insurance certificate at a police station at the last moment. She had been stopped in her car in October 2000.
On Tuesday she won the Television and Radio Industries Club satellite and digital TV award.
Van Outen, who recently split with her boyfriend, Jamiroquai singer Jay Kay, had been relatively quiet since being lured back to star alongside Johnny Vaughan on The Big Breakfast until the end of his contract in January.
Undaunted
"When I left the Big Breakfast I thought I would take some time out but I started to get itchy feet," she said.
"I had been to see Chicago and just thought it was fantastic, so I rang my agent and got him to find out when they were re-casting.
"I knew it would be tough and I had to work really hard."
She will have to adopt and American accent to play the touch Roxie Hart in the musical, which won the 1998 Olivier Award for Outstanding Musical Production.
She will also have to sing as the show includes the songs All That Jazz, Razzle Dazzle, Class and All I Care About, but Van Outen is undaunted.
"The singing is not such a problem because you can practice singing anywhere but the dancing is tougher, especially when you haven't danced professionally for ten years," she said.
Van Outen's acting credits include appearing in the sitcom Babes in the Wood and the film Love, Honour and Obey.
She will be joined in Chicago by James Gaddas - currently to be seen in Yasmina Reza's hit play Art - who to take over the role currently played by Sacha Distel.
Distel is leaving to work on a forthcoming musical about Maurice Chevalier.