Gay will join the Association of British Insurers as director of life, savings and protection.
The Rt Hon John Gummer, chairman of AIFA, said: “During a difficult economic year for members, AIFA and AMI have continued to provide a strong and essential voice for their professions.
“AIFA has reduced its costs, while increasing revenues, and has improving operations and governance.
“AIFA is now in a better position to provide the single, strong and united voice that is able to exert greater influence on regulators and policy makers in the UK and Europe.
“Stephen's leadership has been crucial to AIFA's improvement over the past year. I would like to take this opportunity to thank him for his valuable contribution to our work and the development of the itermediary profession.”
Gay said: “I am proud of the work that AIFA and AMI do for their members and what we have achieved during the past year.
“I am also extremely grateful for the support shown by our council and boards, and the dedication of all the staff at the organisation during what has been a difficult year for advisers.
“I have no doubt that AIFA will continue to offer the profession an effective voice that is both listened to and respected by regulators and policy makers now and into the future.”