A New Day... Live in Las Vegas features thirteen live tracks from Dion's successful Las Vegas show, called A New Day... and two previously unreleased studio tracks: "You and I" and "Ain't Gonna Look the Other Way." It was also released with a bonus DVD containing 45-min documentary, called One Year... One Heart.
The French edition of A New Day... Live in Las Vegas contains "Contre nature" as a bonus track.
The originally scheduled Live in Las Vegas - A New Day... DVD release date (autumn 2004) was postponed because of changes and improvements made to the show since the initial filming. A New Day... was re-shot in high-definition during the January 17–21, 2007 week and released on December 7, 2007. The two disc DVD contains more than 5 hours of never-before seen footage, including the concert and three exclusive documentaries. Live performances of "Nature Boy," "At Last," "Fever," "Et je t'aime encore" and "What a Wonderful World" are available only on A New Day... Live in Las Vegas CD, as they were removed from the show at the time of filming the DVD.
The album met with positive reviews. AllMusic said that "this live document of the Las Vegas show drives home the point that Celine is one of the most potent entertainers in adult contemporary music." According to them Dion is "equally as comfortable in high-tempo numbers chock-full of her signature vocal acrobatics as she is in quiet, contemplative moments. It's an ideal souvenir for those who have experienced the magic with their own ears and eyes. And while it's not the most definitive document of Dion's career, it certainly is a stirring testament to her accomplishments as the standard to whom most vocalists aspire."
A New Day... Live in Las Vegas has sold 530,000 copies in the United States and was certified Gold by the RIAA. It was also certified Silver in the UK. The album reached top ten in many countries, including number one in Greece, number two in Canada, number four in Belgium Wallonia, number seven in Belgium Flanders, number nine in France, and number ten in the United States.