The 18-year-old singer was reported to have proposed to Evans on 1 April, the DJ's 35th birthday, in Paris.
The couple had planned to wed at Evans's £6m mansion near Godalming, Surrey.
But they brought the wedding forward by more than four months to avoid intense publicity and married on Sunday evening.
Virgin Radio DJ Nick Abbot confirmed the news on air at 1745 BST on Monday.
A spokeswoman for Virgin Radio said: "We are delighted to formally announce that Chris Evans and Billie Piper have married."
The ceremony took place in Las Vegas yesterday at 1815 local time with close friends in attendance, she said.
April Fool's Day
"Virgin Radio knew of their intention to marry last week but we were sworn to secrecy," she added.
"We wish Chris and Billie every happiness and look forward to celebrating with them when Chris returns to the breakfast show next Monday."
News of the couple's engagement was broken in April.
The 18-year-old singer was reported to have proposed to Evans on 1 April, the DJ's 35th birthday, in Paris.
The £200 wedding ceremony took place at the Little Church of the West on the Las Vegas strip and was conducted by a local minister, the Reverend James Hamilton.
Church manager Greg Smith said the couple looked "ecstatic". They had six guests including Danny Baker, who was their best man, he added.
Evans was wearing striped trousers and a green shirt, Mr Smith added, while Billie wore a pink sarong and white cotton blouse.
The couple are the latest in a string of celebrities to marry at the Little Church of the West, including Bob Geldof and Paula Yates; Noel Gallagher and Meg Mathews; and Richard Gere and Cindy Crawford.
Others to marry there have included Zsa Zsa Gabor, Judy Garland, Mickey Rooney, Telly Savalas, Johnny Hallyday, and Dudley Moore.
The chapel was built in 1942 from cedar and Californian redwood.
The cost of a wedding starts at 65 dollars (£45) for the hire of the church, with other options available, including a tape of the ceremony at 10 dollars (£7), a garter for the bride at 7.50 dollars (£5) and the services of an organist for 30 dollars (£20).
Painful break-up
The package Billie and Evans chose includes the organist, the tape - with a five-minute history of the chapel and a customised wedding certificate and holder, 10 glossy photographs, a teardrop rose bouquet for her and buttonhole for him.
Billie, from Swindon in Wiltshire, met Evans while appearing on his television programme TFI Friday in May 2000.
She was going through a painful break-up with Ritchie Neville of hit boy band 5ive.
But romance with Evans blossomed after she went on his radio breakfast show in December to promote her single Walk Of Life.