During his two years as chairman Hathaway will lead the MAA's 'Transformation Britain' agenda, which is designed to help its member agencies and their clients develop the tools they need to take advantage of how comms is changing.
Hathaway's succession to the chairmanship was confirmed by a vote at the MAA's AGM last night. He already served on the organisation's board as chair of international development.
Before joining Cheil in 2010, Hathaway was the EMEA chief executive of Saatchi & Saatchi X for three years and chairman of its global creative board. He was previously the managing director and then chief executive of Saatchi & Saatchi X UK.
Hathaway said: "Our 'Transformation Britain' manifesto addresses the disruption and challenges that businesses face at its core, because this is the biggest driver behind the change of agency and client relationships.
Through supporting our agency membership in embracing those challenges, we aim to bring clients and agencies closer together than ever before and ensure that our creative industry continues to be a bedrock of the British economy."
Millner, the global chief executive of Iris, became chairman in 2011. He was originally going to serve in the post for two years, but he extended that to three in May 2013 to provide consistency after the MAA took on new members and expanded its board.
Scott Knox, the managing director of the MAA, said: "Simon's strategic expertise in global retail and marketing is exactly the right fit for the MAA's 'Transformation Britain' agenda, and we have complete faith that he will continue the brilliant foundations that Ian Millner has lain in the past three years."
Initiatives during Millner's tenure included 'Marketing 4 Start-Up Britain', which supported entrepreneurialism, and the 'Future Leader's Academy', an initiative giving providing younger people in the industry the opportunity to learn from senior executives.