Copywriter Ewart and art director Sullivan are its first creative appointments, and will work alongside the agency's founding partners, Sean Doyle, Dave Dye and Walter Campbell, across the agency's portfolio.
Dye said: "Dave and Tom are 100 per cent into the work. They've got a lot of nice work under their belt, but they're still hungry."
The duo, both aged 24, were ranked among the industry's best young creative teams in Campaign's 2002 Book of Lists.
They wrote and art directed AMV's BBC ad showing a man racing home over building rooftops to watch television, worked on the agency's Drink Drive account for COI Communications before it moved to D'Arcy last year and also penned ads for Volvo.
The team was at AMV for two years.
"Leaving AMV was a tough decision to make. We've enjoyed our time there immensely and had the opportunity to work with some very nice and talented people, but Walter made it easier when he pointed out that CDD is within spitting distance of five smashing boozers," Ewart said.
The appointment comes as CDD beds in new accounts alongside its founding Mercedes client. Last year, it picked up briefs for Sekonda Watches, Merrydown and McCain.
The CDD managing director, Alison Hoad, said: "Tom and Dave are undoubtedly good creatives but, equally importantly, they are a good fit for CDD. We're also looking for rising stars in other disciplines."