The brief is to plan the homes to be built by 2031, along with provision for the creation of 28,000 jobs to sustain the community.
The Prince's Foundation, a charity that exists to promote the Prince of Wales' views on Urban Design and architecture, had been working with American multidisciplinary consultant URS and Miami-based architect Duany Plater-Zyberk & Company on the project.
A team featuring EDAW and HTA Architects was understood to have come second in the competition.
The other teams were led by Dutch architect Kuiper Compagnons and HOK Architects.
The codes will ensure all new housing faces on to a public space
Marcus Wilshere, Urban Initiatives
Urban Initiatives director Marcus Wilshere said that the firm's task, scheduled to last a year, would be to produce a plan detailing the use of land to the south and west of the town.
He said: "What we'll produce for Ashford is clear guidance of routes and connections and what priorities the area will have."
Wilshere added that part of the brief drawn up by the client, English Partnerships, stipulated that the masterplan should follow design codes currently being championed by John Prescott.
The codes will include structural requirements for housing density and percentages of affordable homes, but also offer guidance on materials that should be used to make the developments work as a community.
Wilshere added: "The codes will be concerned with matters such as ensuring all the new housing faces on to a public space."
Urban Initiatives also triumphed in another masterplanning competition to provide a local development strategy for Laurieston, west of the Gorbals near Glasgow city centre.