Engine will work with Agenda, a public affairs consultancy based in Washington DC, to provide Nato with strategic comms advice, and support on design, branding, advertising, marketing, PR, broadcast video, digital and social media.
The two agencies have signed a five-year agreement with Nato (the North Atlantic Treaty Organisation) following a competitive pitch.
Simon Peck, the group managing director of Engine UK, said: "We are excited to be working with such an illustrious and important institution, as it tackles some of the most fascinating challenges of our time."
"This is a huge win for our team," said Agenda founding partner Doug Turner. "This was a long and highly competitive process and we are honored to have the chance to do important work for such a storied institution, and equally pleased to be partnered with Engine on this effort."
He added: "There is no greater challenge – and reward – than helping the Alliance deal with a new generation of security threats."
Nato is headquartered in Brussels and was founded in 1949.
In the past, Nato has used M&C Saatchi to advise on its communications for its Allied Rapid Reaction Corps.