Klonhammer joins from 180 Amsterdam and will be responsible for helping to strengthen Grey's offering to international clients.
She will work closely with the agency's executive creative directors, Colin Lamberton and Seyoan Vela, who joined the Amsterdam shop from Grey's London office in May, and will report directly to Carolyn Carter, the chief executive of Grey Group EMEA.
Klonhammer said: "With Colin and Seyoan in the lead, I feel confident we can make Grey Amsterdam a creative powerhouse."