The Inter-Religious Organisation (IRO) had its beginnings as the Inter-Religious Organisation of Singapore and Johor Bahru which was officially launched on 18 March 1949. It was renamed the Inter-Religious Organisation of Singapore in 1961.

When Maulana Abdul Aleem Siddiqui, a well known Muslim missionary, visited Singapore in 1949, an inter-faith reception for him sparked the idea for an inter-faith organisation. Sir Malcolm Macdonald, then the British Commissioner General for Southeast Asia, helped to propel this vision into reality.