In later life, Mahmoud Khayami was active as a philanthropist and collector of fine Persian art, forming the Khayami Collection. He promoted inter-religious relations in the UK, and internationally, with a special emphasis on relations between the Jewish, Christian, and Muslim communities. Among his activities was the hosting at Chatham House (RIIA) of inter-religious conferences. He was involved with the Encyclopædia Iranica project and chaired the board of editors.