The brief involves providing strategic comms support for The International Quarter, a £2.1bn development in Stratford that will offer four million square feet of commercial office space.
Fishburn was appointed after a competitive pitch.
The agency's PR activities will span consumer, business and property comms as well as public affairs, stakeholder relations and event support.
The account will be led by corporate managing director Dominic Pendry, and his team includes senior consultant Ben Lyons and consultant Ludo Baynham-Herd.
Pendry said: "We will be working to challenge perceptions of the modern workplace. Fishburn is committed to doing impactful work that makes a real difference to clients’ bottom line and this project is the perfect fit.
"The win adds to our substantial experience of the property, infrastructure and regeneration industries, providing further evidence that clients need agency partners who can advise across all areas of their business, and deliver strategies grounded in strong intelligence and insights."
Businesses are expected to start moving into the commercial district starting in 2017, with Transport for London signing a pre-let agreement. In total, more than 25,000 office workers are expected to work in the business district once it is completed.