Molner, 50, popped the question over the holiday weekend on a beach in East Hampton, New York.
Couric, 56, was previously married to Jay Monahan, who died from colon cancer back in 1998.
She took to her Twitter page to confirm the news, saying "Yes it's true! So touched by all the kind Tweets & warm wishes-thank you! A great end to the summer & looking fwd to seeing you all Monday!"