The Eastern and Coastal Docese is a member of
Evangelical Lutheran Church in Tanzania (ELCT)
Kanisa la Kiinjili la Kilutheri Tanzania (KKKT)

Via ELCT the diocese is involved in 
* Christian Council of Tanzania (CCT)
* The Lutheran World Federation (LWF)
* All African Conference of Churches (ACC)
* World Council of Churches (WCC)

ECD is also a member of
United Evangelical Mission (UEM)

UEM member churches in the Africa region
Eastern and Coastal Diocese of ELCT(ELCT/ECD), Karagwe Diocese of ELCT(ELCT/KAD), North-Eastern Diocese of ELCT(ELCT/NED), North-Western Diocese of ELCT(ELCT/NWD), Evangelical-Lutheran Church in Botswana (ELCB), Rhenish Church South Africa (RC-SA), Uniting Reformed Church in Southern Africa (URCSA), Church of Christ in Congo (ECC), Baptist Church in Central Africa (CBCA), The Community of Disciples of Christ in Congo (CDCC), Association of Evangelical Churches of the Lulonga River (CADELU), Evangelical Church in Cameroon (EEC), Evangelical Lutheran Church in the Republic of Namibia (ELCRN), Anglican Church of Rwanda (EAR), Presbyterian Church of Rwanda (EPR)

UEM member churches in Asia
Chinese Rhenish Church Hong Kong Synod (CRC), Batak Christian Community Church (GPKB), Kalimantan Evangelical Church (GKE), Protestant Christian Pakpak Dairi Church (GKPPD), Indonesian Christian Church (HKI), Christian Church of Northern Central Java (GKJTU), East Java Christian Church (GKJW), Christian Protestant Angkola Church (GKPA), Karo Batak Protestant Church (GBKP), Christian Protestant Church in Indonesia (GKPI), Nias Christian Protestant Church (BNKP), Protestant Christian Church in Mentawai (GKPM), Simalungun Protestant Christian Church (GKPS), Batak Protestant Christian Church (HKBP), Evangelical Christian Church in Tanah Papua (GKITP), United Church of Christ in the Philippines (UCCP), Methodist Church of Sri Lanka (MC-SL)

UEM members in Germany
Evangelical Church of Hesse and Nassau (EKHN), Evangelical Church of Hesse-Waldeck (EKKW), Evangelical Church in Rhineland (EKiR), Evangelical Church of Westphalia (EKvW), Evangelical reformed Church (ErK), Church of Lippe (LL), v. Bodelschwingh Foundations Bethel (vBS)