The train operator, which called the pitch in October, said the new identity would strengthen its presence in a "changing and competitive" market.
It is likely to face challenges from European operators such as Deutsche Bahn following the EU's liberalisation of rail lines from January 2010, removing Eurostar's cross-channel monopoly.
The London-based agency will create a new identity for Eurostar which will work alongside the planned redesign of the trains' interiors and exterior livery by Italian designer Pininfarina. The first new-look trains are due in service in 2012.
Nick Mercer, Eurostar's commercial director, said: "We are very pleased to be working with SomeOne who have demonstrated a real understanding of the Eurostar brand and service personality.
"We are confident that with their creative input, our new visual identity will capture the innovative and pioneering spirit of our brand and will strengthen, refresh and reinforce Eurostar's presence within a changing and competitive market."