The IRO was founded in Singapore shortly after the Second World War in 1949. His Eminence Maulana Mohamed Abdul Aleem Siddiqui visited post-war colonial Singapore early in the year and some 40 personages gathered and heard his message of peace at the invitation of the Muslim Missionary Society. The guests included His Excellency the Rt. Hon. Malcolm MacDonald, the Commissioner General for Singapore as well as representatives of the Buddhists, Hindus, Sikhs, Christians and Jews. They were catalyzed by the success of the occasion and planned to meet again in order to bind a fellowship of peace together.
In a series of 2 further meetings in February 1949, the Maulana proposed the formation of a body to represent all religions and a Consultative Committee formed to draft and adopt the constitution of the Inter-Religious Organisations of Singapore and Johore Bahru. The IRO was to be open to leaders and laymen of all the various religions of Malaya with peace and goodwill as its objective.
On 18th March 1949, the IRO’s first public meeting was held at the Victoria Memorial Hall, Singapore, before a huge audience of about 2,000. Speeches for religious harmony were given by Rt. Hon. Malcolm MacDonald, the Commissioner General of Singapore, who became its first Patron; Rev. Dr H.B. Amstutz, who was in turn IRO’s first President; H.E. Maulana Mohamed Abdul Aleem Siddiqui; Sri Mehervan Singh for Sri Kartar Singh; Swami Vamadevananda of the Ramakrishna Mission; and Sim Boon Hwee for Rev. Sek Hong Choon. Their words were soon published as “The Contribution of Religion to Peace” MPH 1949. This book has since been reprinted in 2014.

The newly formed IRO had an active first year in 1949. During the year more religious bodies joined the IRO as representative membership opened.1 The IRO had held four public meetings by the end of the year. In these meetings religious unity and harmony were discussed with speeches by leaders representing the different faiths.2
As part of the international inter-religious movement for harmony, the IRO was invited to the World Conference of Religions and Peace (WCRP) first assembly, Kyoto, 1970. As a need was seen for an Asian body, the WCRP was led to set up the Asian Conference of Religions and Peace (ACRP, a.k.a. Religions for Peace Asia) and the IRO hosted its founding meeting in Singapore, 1976.7 The conference opened at the Regional English Language Centre on 25 Nov 1976 for a week, with some 300 delegates and observers representing the major religions of 19 countries.8 The IRO continues to receive visits from different religious leaders and government officials from around the world and also participates in study visits to other countries.
When the IRO was founded in 1949, its constitution provided that the council would be composed of: Muslims, Protestants, Roman Catholics, Buddhists, Hindus, Confucianists, Sikhs, Jews, and miscellaneous. That foresight of the IRO founders made provisions for the growth of the IRO membership to include the followers of minority faiths. More religious faiths became part of the IRO as diversity in religious harmony has spread in Singapore; Zoroastrianism officially in the IRO from 1961, the Taoism and the Baha’i Faith in 1996 and Jainism in 2006.