The Modern Family actress announced the news via her Twitter page on Wednesday, accompanied by a photo of herself as she posed during a shoot for the cosmetics brand.
Talking with People, she expressed her excitement at the new role and admitted that it has fulfilled one of her lifelong dreams.
"It feels amazing. I've always wanted to be a CoverGirl. I always loved seeing the pictures of the campaigns in magazines," she explained. "I've always had a very good relationship with makeup; it's one of my favourite things."
Vergara went on to say that joining CoverGirl means a lot to her as it will allow younger Latina girls to see an identifiable face in print.
"When you grow up, you look up to girls in the magazines, and you never think you're going to be that pretty, or that well made-up, or that glamorous," she added. "I love that I have the Latin flavour; Latin girls can relate to me, see what I'm wearing, see my makeup, my hairstyle."
The star's ads for CoverGirl will debut in January 2012.
Vergara recently expressed frustration over claims that photos for her Pepsi ads had been photoshopped to make her appear thinner.
She previously insisted that she hates working out but does it in order to maintain her health.