Euro will set up a subsidiary company - Euro Referendum - to service the business.
Its name reflects the Tories' pledge to hold a referendum on the EU treaty should they win power. The team will be headed by the agency's global chief operating officer, Chris Pinnington; the UK group chairman, Kate Robertson and the executive creative director, Mark Hunter.
The Conservative Party head of brand communications, Anna-Maren Ashford, said: "Euro RSCG has already brought a huge amount of energy and passion to this challenge and we're very pleased to be working with it."
The Euro RSCG Worldwide chief executive, David Jones, added: "You can work on many exciting brands, but nothing has the same important scale as being part of getting a new government elected."
Euro has already produced its first work for the party to capitalise on Gordon Brown's decision not to hold a snap general election. It created bottles of beer with a "Bottler Brown - zero strength" label, and placed people in bottle suits at outside broadcasts covering the news as it broke over the weekend.