Call centre worker Connie Fisher has won BBC One's talent search How Do You Solve a Problem Like Maria?
The win secured Connie a starring role in the West End
She went head-to-head with Helena Blackman in the final for the chance to take the lead in Andrew Lloyd Webber's stage revival of The Sound of Music.
After a viewers' vote, the 23-year-old from Pembrokeshire in west Wales landed the West End role.
An average 7.7 million viewers tuned in to watch the result announced by host Graham Norton.
Connie has unsuccessfully been auditioning for parts since graduating from theatre school in London.
She said: "Every night will be an opening night".
She was the bookmakers' favourite to win the six-month contract.
Connie was open-mouthed and close to tears when Norton announced the result after more than two million votes.
"Just thank you to everybody who's voted," she said, before going on to perform the show's title song for the studio audience.
"I look forward to every performance that I give you. Thank you for making my dreams come true."
She says Julie Andrews, who played the part of Maria in the hugely successful film version of The Sound of Music, is her heroine.
Earlier in the evening, Siobhan Dillon, one of three remaining hopefuls left on the show, was voted off.
The show has been hosted by Graham Norton
Lord Lloyd-Webber launched the televised search for a lead actress after failing to secure Hollywood star Scarlett Johansson for the lead role after holding initial talks.
He has been chairing a panel of judges on the show, whittling down thousands of singers who auditioned down to a final 10 who have been battling it out in live performances for a place on Saturday's final.
Before the result was revealed, he said Connie was his choice for the part.
The musical is set to open at the London Palladium on 14 November.
There have been press reports that Lord Lloyd-Webber has already signed up a professional theatre actress to share the leading role with Connie.