Dare won the business after a pitch, run by ISBA, that began in October last year.
The agency will initially help develop the Metro brand and positioning for its digital platforms and products as the publisher delivers its "mobile-first" strategy.
Bryan Scott, the marketing communications director at Metro, said: "We have a clear focus to help urbanites get more from their city life and Dare will be instrumental in helping us shape our brand communication and product messaging."
Metro recently relaunched its website and has apps for Android phones, Kindle Fire, iPad and iPhone. See also Inside Metro.