Miller, 29, named a Campaign Face to Watch this year, has been at the agency for the past five years, working across clients including Nestle, Boots and Kraft.
In 2003, her paper on Kit Kat scooped the Account Planning Group Grand Prix prize and a gold in the "established brands over £5 million" category.
In 2001, a paper she wrote on Boots won bronze at the same awards.
Miller will report directly to Charlie Snow, DLKW's planning director.
Snow said: "I'm delighted we can attract talent this good to DLKW. She embodies values that we hold very dear: she's clever and down-to-earth and she cares about good communications."
Miller said of her move: "I've learned a huge amount from my friends at JWT, and have lots of good memories to take away with me, but the opportunity to work with Charlie and his colleagues at DLKW at this stage in their trajectory was far too good to pass up."
Miller started her career at Delaney Fletcher Bozell, where she worked for two years before joining JWT.
Miller will work on DLKW's Burger King and Halifax accounts.