The Mar Thoma Syrian Christian Community of Kerala was an autonomous Church in the unity of the Catholic Church, ever since its foundation in 52 A.D by St. Thomas, the Apostle. They remained one body and flourished in the course of years. But in the seventeenth century, due to the intervention of the Portuguese missionaries a schism occurred. A good section of the Syrians eventually became Jacobites under the Patriarch of Antioch.

Ever since the schism, attempts at reunion were made. On September 20, 1930 the Reunion Movement took shape with the reunion of two eminent Jacobite Prelates, the late Archbishop Mar Ivanios and late Bishop Jacob Mar Theophilos. It was a triumph of ecumenism as their reunion took place as a church accepted with its liturgy, customs and jurisdiction. Thus it prepared a way for a complete reunion of the Jacobite-Orthodox Church of Kerala.

As the Reunion Movement developed speedily, Pope Pius XI established the Malankara Hierarchy for the reunited people and established the Archdiocese of Trivandrum and the Diocese of Tiruvalla by the Apostolic Constitution, Cristo Pastorum Principi dated June 11, 1932.

Accordingly the Diocese of Tiruvalla was established on November 6, 1933 and Rt. Rev. Jacob Mar Theophilos was enthroned as its first Bishop. He was called for his eternal reward on 27th June 1956. His Excellency Most Rev. Thomas Mar Dioscoros Metropolitan reunited with the Diocese of Tiruvalla from the Knanaya Jacobite Church on 12 November 1939 and led a private life at Thirumoolapuram. He passed away on 21st February 1943. His Grace Most Rev. Joseph Mar Severios, Metropolitan of the Niranam Diocese of the Orthodox Church reunited with the Malankara Catholic Chuch on November 29, 1937. Due to the ill-health of Mar Theophilos the Holy See appointed His Grace Joseph Mar Severios as the Apostolic Administrator of the Diocese of Tiruvalla in 1938. He was appointed the Bishop of the Diocese of Tiruvalla in 1951. He was called for his eternal rest on 18th January 1955. The Holy See appointed Reverend Father Cherian Polachirackal Auxiliary to the Bishop of Tiruvalla. His consecration was on 22nd April 1954 and he took the name Zacharias Mar Athanasios. The Diocese was extended from the river Pampa in the south to the river Ponnani in the north and from the Arabian Sea in the west to the Western Ghats in the east. The Diocese was further extended to the north from the river Ponnani by the decree of the Sacred Congregation for the Oriental Churches, by Prot N.534/43 dated February 14th 1958 and brought under it the whole of Malabar region of Kerala, the civil districts of Coimbatore and Nilgiris and Karoor Taluk in Triuchirappally District of Tamil Nadu and the districts of Mysore, Mandya, Coorg, Hassan, Chickamangalore, Shimoga and South Kanara of Karnataka State. His Excellency Zacharias Mar Athanasios entered into eternal rest on 28th September 1977. Rt. Rev. Msgr. Mathew Nedungattu was elected the Administrator.

His Holiness Pope John Paul II by the Apostolic Constitution of October 1978 separating the civil districts of Malappuram, Kozhikode and Kannoor of Kerala, Nilgiris of Tamil Nadu and Coorg, Mysore, Mandya, Hassan, South Kanara, Chickamangalore and Shimoga of Karnataka from the Diocese of Tiruvalla, established the new Diocese of Bathery and appointed His Excellency Most Rev. Cyril Mar Baselios as its first Bishop. The official inauguration of the Diocese was on 2nd February 1979. Very Reverend Father Isaac Koottaplackal was appointed Bishop of Tiruvalla to succeed His Excellency Most Rev. Zacharias Mar Athanasios. His consecration took place on 28th December 1978 at Mar Ivanios Nagar, Thirumoolapuram and he received the name Isaac Mar Youhanon.

His Holiness Pope John Paul II sent His Eminence Cardinal Wadislaw Rubin, the Prefect of Sacred Congregation for the Oriental Churches as his delegate to the golden jubilee celebration of the Reunion Movement, held in December 1980 at Kottayam in the Diocese of Tiruvalla. The golden jubilee of the establishment of the Diocese was celebrated in January 1984 at St. John’s Cathedral, Tiruvalla. Mar Youhanon was called for eternal peace on 28th April 1987. Rev. Fr. George Chundevalel was elected the Administrator who later was appointed the Bishop of the Diocese with the name Geevarghese Mar Timotheos. His consecration took place on 6th August 1988 at St. John’s cathedral, Tiruvalla.

His Eminence Achille Cardinal Silvestrini, the Prefect of the Congregation for Oriental Churches visited the Diocese in February 1996. Reverend Father Mammen Chackalapadickal was appointed Auxiliary to the Bishop of Tiruvalla. He was consecrated Bishop on the 17th July 1997 at St. John’s Cathedral, Tiruvalla with the name Thomas Mar Koorilos.

The septuagenial of the Reunion Movement was celebrated at Tiruvalla on 27th December 2000. The Patriarch of the Syrian Catholics in Antioch and the present Prefect of the Congregation for the Oriental Churches, His Eminence Cardinal Ignace Moussa Daoud was the chief guest.

His Holiness Pope John Paul II bifurcated the Diocese of Tiruvalla and established the new Diocese of Muvattupuzha, which includes the revenue Districts of Ernakulam, Thrissur and Palakkad of Kerala. The new diocese was inaugurated on 6th February 2003 and His Excellency Most Rev. Dr. Thomas Mar Koorilos was appointed by the Holy Father as the first Bishop of Muvattupuzha. On 29th March 2003 the Holy See accepted the resignation of His Excellency Geevarghese Mar Timotheos from the diocesan administration due to super-annuation. Rev. Dr. Stephen Thottathil was elected the Administrator. The Holy See appointed His Excellency Most Rev. Dr. Isaac Mar Cleemis as the sixth Bishop of the Catholic Diocese of Tiruvalla on 11th September 2003. His Excellency Isaac Mar Cleemis took charge of the Diocese on 2nd October 2003 at St. John’s Cathedral, Tiruvalla. The newly built St. John’s Cathedral was consecrated on 20th and 21st of September 2004 by His Grace Cyril Mar Baselios, the Metropolitan Archbishop of the Malankara Catholic Church.

His Eminence Cardinal Ignace Moossa Daoud paid a visit to the Diocese on the 12th May 2005. The Holy Episcopal Synod of the Malankara Catholic Church decided on 3rd December 2005 to elevate the Diocese of Tiruvalla to the status of an Archdiocese with the Dioceses of Bathery and Muvattupuzha as its suffragans, and the Bishop of Tiruvalla as Metropolitan Archbishop. With the consent and blessings from the Holy See, His Beatitude Moran Mor Cyril Baselios Catholicos, the Major Archbishop of the Malankara Catholic Church, announced the proclamation on 15th May 2006 at St. John’s Cathedral, Tiruvalla. His Grace Most Rev. Dr. Isaac Mar Cleemis was installed as the first Metroplotan Archbishop of the Archdiocese of Tiruvalla on 10th June 2006 at St. John’s Metropolitan Cathedral, Tiruvalla. His Beatitude Cyril Baselios the Major Archbishop-Catholicos was the main Celebrant and about thirty Bishops and a vast group of civil and social leaders and thousands of faithful participated in the Installation Ceremony.

Bishop Thomas Mar Koorilos, of the Muvattupuzha Diocese, was installed as the second Metropolitan Archbishop of Tiruvalla at a ceremony held at St. John's Cathedral in Tiruvalla on Wednesday 2nd May 2007. He was appointed as the Archbishop of Tiruvalla on 26th March, 2007.

Major Archbishop Baselios Cleemis Catholicos was the principal celebrant of the installation ceremony. The installation service was held amidst the holy Eucharist celebrated by the Catholicos, assisted by Bishops Geevarghese Mar Divanyasios, Joshua Mar Ignatios, Joseph Mar Thomas, Youhanon Mar Chrysostum, Geevarghese Mar Timotheos and Yakoob Mar Barnabas.

Hundreds of faithful thronged the cathedral premises to witness the installation ceremony on 2nd May 2007 . The holy Eucharist began at 8.15 a.m. and the installation ceremony at 9.45 a.m.

The order of the Catholicos appointing Mar Koorilos the Archbishop of Tiruvalla was read out by Chancellor of Thiruvananthapuram Archdiocese Fr. Antony Valiyavilayil. The Catholicos blessed the new Archbishop and handed over the pastoral staff to him, later, marking the culmination of the installation ceremony.