The 'Starry Eyed' singer, 26, wore the barely-there outfit at Andrea's Restaurant before her DJ set at Surrender Nightclub in Las Vegas' Wynn Hotel.
She revealed her glowing summer tan in the black skintight shorts and bra top, which she teamed with a biker-style jacket and flat black lace-ups.
She also debuted her new shorter hairstyle.
Ellie, who is dating War Horse actor Jeremy Irvine, is currently in the US on a promotional tour and tweeted: "To LA, Vegas, LA! Been waiting for this! I'm even more excited now."
After DJing, Ellie shared her feelings about the set, tweeting: "Enjoyed that so much. Thank you Surrender."
Ellie is promoting her single 'Burn' which is currently in the top 10 of the US iTunes chart.
The song was originally recorded by Leona Lewis for her album Glassheart, before being cut from the final track listing and is the first single from Ellie's re-release of Halycon Days.
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Watch the video for Ellie's video 'Burn' below: