He is being replaced by two people: Thomas Buberl will take over as chief executive while Denis Duverne will become chairman.
The decision to split the role was agreed unanimously at a special meeting held on Saturday.
Buberl will join the group head office in Paril from today, initially working as deputy chief executive alongside de Castries and Duverne to finalise Axa’s new strategic plan, which is expected to be made public on 21 June, as well as ensuring a smooth handover period.
De Castries said: "It has been a privilege to succeed Claude Bébéar and lead Axa over all these years, and I want to express my gratitude to the 166,000 women and men who are the face of Axa for our 103 million clients across the world - their professionalism and engagement have been a driving force and a fantastic motivation for me."
In a letter to staff, he added: "In the wake of our success in achieving our Ambition Axa plan, and before we enter into a new strategic cycle, I considered, with the support of the board, that it was the best moment to begin the transition to a new management team who I know will very successfully lead Axa through the next stages of its development. While I will leave the group with great emotion, I am very happy and confident to see Thomas take over the executive management of Axa.
"He has the experience, leadership skills and values to seize the opportunities offered by a rapidly changing world, and to make Axa a company that is always closer to its clients - which will be the key of our long term growth."
Speaking on behalf of the board of directors, Norbert Dentressangle added: "In 2015, while progressing on the execution of an intense digital transformation, Axa successfully achieved its five-year strategic plan, and delivered record underlying earnings, which represents an eightfold increase during Henri de Castries' tenure as chief executive.
"The board of directors would like to pay him a strong and well-deserved tribute for his actions, and extends its very warm thanks to Denis Duverne who, as deputy chief executive, has been instrumental in Axa’s strategic decisions and strengthening the group’s solidity. Together, they leave to the new leadership team a very well-managed, extremely resilient group, with high quality and engaged employees."