The FRCSA strive towards unity in doctrine, worship and discipline with churches in South Africa and elsewhere in the world that exhibit the marks of a true church (as indicated in art. 29 of the Belgic Confession) not only on paper, but also in the everyday practice of church life. At local level there are currently promising negotiations in Pretoria between the FRCSA congregations Pretoria and Pretoria-Maranata, with the RCSA congregations Die Kandelaar, Totiusdal and Oos-Moot. In addition the FRCSA have good contacts with the Free Church of Southern Africa.
Internationally there are sister church relationships with:
From 2017 there was only a restricted sister-church relationship with the GKv (RCNL). Synod Belhar 2021 of the FRCSA decided that the sister-church relationship will come to an end when the GKv unites with the Nederlands Gereformeerde Kerken (NGK).
That unification has taken place on 1 May 2023, and as a result the FRCSA have no more sister-church relationship with the GKv (RCNL) from that date.
The FRCSA is also a member of the International Conference of Reformed Churches (ICRC), bringing together several Reformed churches from around the world.