The 'Stronger' hitmaker, who married music manager Brandon Blackstock just last month, announced the news on Twitter yesterday (19.11.13).
The 31-year-old tweeted: "I'm pregnant!!! Brandon and I are so excited! Best early Christmas present ever :)"
Kelly postponed a gig in Buffalo, Tennessee due to "illness" on Saturday night and said she was "trying to get better".
She is believed to be suffering from morning sickness and fans tweeted their support.
One wrote: "SO happy for you two!! Congrats! It gets easier after the 1st trimester, I promise! :)."
Using a reference from the film 'Elf', she joked: "I'll believe it when it happens, but so far you sit upon a throne of lies ha!"
The former 'American Idol' winner recently admitted to Jay Leno that her and Brandon couldn't wait to have a baby.
She said: "We're trying, trying, trying ... like rabbits! I want a little baby with little feet and I just want to bite them."
Brandon has two children from a previous relationship, Savannah, 11, and Seth, seven who where the only guests at the couple's wedding on October 20 at Blackberry Farms in Walland, Tennessee and Kelly said being a stepmother to the pair has made her more maternal.
She added: "They're so great. I never wanted kids before, but now I want, like, five."