In the history of Rissho Kosei-kai, the interreligous cooperation movement leading toward the establishment of the WCRP began in May 1965. That year, a special papal envoy traveled to Japan and invited the late founder, Rev. Nikkyo Niwano, to attend the last session of the Second Vatican Council as a special non-Christian guest representing Japanese religious circles. He was received by Pope Paul VI in private audience during the period of the council.

In their meeting, the pope said to him, "In the Vatican, too, the attitude toward non-Christian religions is changing. It is important for people of religion not to cling to factions or denominations, but to recognize each other and pray for each other." Rev. Niwano later said he then realized that the Buddhist must pray for the Christian, and the Christian for the Buddhist. Otherwise, there will be no way for religions to contribute toward world peace. At this historic meeting, Rev. Niwano was wholeheartedly convinced that his mission was to realize world peace through interreligious dialogue and cooperation. With that conviction, he began his utmost efforts to establish the basis for interaction and dialogue among the world's different religions.

As one of the founding members of the WCRP, he vigorously traveled the globe and met key religious leaders to encourage them to join the first assembly of the WCRP to be held Kyoto in 1970.

Rissho Kosei-kai has continued to send representatives to the world assemblies held every four or five years. The organization has participated in and actively supported all the assemblies held so far, in Leuven, Belgium (WCRP II) in 1976; Princeton, N.J., USA (WCRP III) in 1979; Nairobi, Kenya (WCRP IV) in 1984; Melbourne, Australia (WCRP V) in 1989; the Vatican and Riva de Garda, Italy (WCRP VI) in 1994; and Amman, Jordan (WCRP VII) in 1999. From 1979, the late founder, Rev. Nikkyo Niwano, was an honorary president of WCRP and Rev. Nichiko Niwano, the president of Rissho Kosei-kai, is currently a WCRP international president.