National Council of Churches Christ USA - An ecumenical consortium of Christian denominations. Mar Thoma Church is an active member of this consortium.

World Council of Churches - A worldwide fellowship of 349 churches seeking unity, a common witness and Christian service. Mar Thoma Church is one of the founding members of this fellowship.

Worldwide Anglican Communion – A fellowship of Christian churches from over 165 countries.

Ecumenical Council of Kerala Churches in Chicago – A Fellowship of Churches that traces their origin from the Apostle Saint Thomas tradition from Kerala, India.

Historical Kerala Churches in Chicago