TBWA\Amsterdam won the business after a competitive pitch, beating Scholz & Friends Berlin and VCCP Berlin. The research company Grupo Consultores ran the pitch through its Madrid office.
There was no incumbent on the account, although Kayak has previously used the New York agency Barton F Graf 9000 for its advertising.
At the beginning of the year, Kayak appointed ZenithOptimedia to handle its digital and offline media planning and buying business across Europe after a competitive pitch.
Simon Neefjes, the chief executive of TBWA\Amsterdam, said: "We are very, very happy with Kayak. It's a very successful and leading technology company with a clear focus and a love for creative work, as already is shown in the great work of Barton F Graf in the US.
"In the pitch process, we have created a SWAT, a creative process using TBWA creatives from six countries to help create the ideas. Because of the opportunity to have direct contact with Kayak's Robert Birge and Stephanie Retchko, we were able to really work together and operate very efficiently."