The pair join from McCann Erickson, where they created the "Jake Courage" integrated campaign to promote the launch of Halo 3 on Xbox. The campaign won a gold Lion at Cannes and gold at the Campaign Big Awards.
In their new roles, they will report to George Prest, DLKW's executive creative director, and will work across a client list that includes Halifax, Morrisons and COI.
At McCann, they also produced the award-winning "Computertan" campaign for the skin cancer charity Skcin.
Before joining McCann, Mitchell and Harris worked separately, at Abbott Mead Vickers BBDO and M&C Saatchi respectively.
Prest said: "I see Cam and Elliot as an integral part of DLKW's drive towards a brave, new, creative future. They could have walked into any agency in town. I'm delighted they chose here."