Incumbent agency Portland, which has held the account for five years, has been invited to re-pitch for the business.
The brief includes internal communications, external and public affairs, media relations and crisis and issues management, and is designed to "build further trust and pride in the airport", a spokesman for Heathrow said.
He continued: "The time is now right to identify the best partner to take Heathrow's communications forward as we focus on supporting operational and commercial colleagues in delivering outstanding performance, transforming customer service and achieving sustainable growth."
The pitch coincides with Heathrow appointing Nigel Milton as director of comms in January, and Josephine Roberts as head of media in June.
Roberts, who was previously head of UK media at McDonald's, takes over from Julia Weir, who had worked for the airport in a variety of roles since 2006.
Reporting to Milton, Roberts has been tasked with overseeing the Heathrow press office, as well as its consumer and film content team strategy.
PRWeek has contacted Portland for comment.