According to strong and living tradition, St. Thomas the Apostle of Christ landed at Kodungalloor (Cranganore), the capital of the then Chera Empire in the year 52 A.D. Persians, Greeks and Romans found Kodungalloor, which was also known as Mussiris or Mahadevarpattanam, at present situated in the District of Trichur, as an important centre for their trade.
St. Thomas preached the Gospel and founded churches wherever he went. According to tradition, the first place of his apostolate was Palayur, the most ancient shrine of the Arch eparchy of Trichur. Palayur had a Jewish colonyfrom pre-Christian era onwards until last few centuries. Trichur can, therefore, rightly be called "the Cradle of Christianity in India". According to the Malabar tradition, seven Christian communities were established by him in different parts of Kerala before he was martyred in 72 AD at Mylapore near the present Chennai. According to the ancient song Ramban pattu the Apostle Thomas ordained and appointed Kepha as the head of the Indian Church at Kodungallur and Paul as Bishop of Mylapore, thus giving shape to the first Indian Christian Hierarchy.
From the 4th century onwards St. Thomas Christians established relationship with the Church of Persia. Bishops who came to India from that Church also had their residence at Kodungalloor while they held the title of the "Metropolitan and Gate of all India". The traditional jurisdiction of the Metropolitan head of the Indian Church was "the whole of India". The 'Metropolitan' changed his residence from Kodungalloor to Angamaly in the 16th century due to certain political reasons. The territorial jurisdiction was slowly limited. After the death of Mar Abraham in 1577 St. Thomas Christians were subjected to the Latin Bishops from 1599 and continued to be so until 1887. The See of Kodungallur, which has its origin from the time of the Apostle Thomas, was suppressed in the year 1886.
H.H. Pope Leo XIII of illustrious memory, by the epoch- making bull "Quod Jam Pridem" of May 20, 1887, separated the Syrian Catholics of Malabar from the Jurisdictions of Padroado as well as the Vicariate of Verapoly and erected for them two Apostolic Vicariates of Trichur and Kottayam. The Vicariate of Trichur had within its territory the most ancient Christian centers like, Kodungalloor and Palayoor and Angamaly. It can be said that Trichur has the indirect continuation of the See of Kodungallur. Mgr. Adolphus Edwin Medlycott was the first Vicar Apostolic of Trichur.
Nine Years later, by the Brief "Quae Rei Sacrae" of July 28, 1896 the same Holy Father after reorganizing the two Vicariates into three, namely, Trichur, Ernakulam and Changanasserry gave Indians of the Syro-Malabar rite as their Vicars Apostolic. Thus, Mar John Menacherry became the first native Vicar Apostolic of Trichur.
The rapid and remarkable progress that the Syrian Catholics made under the Indian bishops in the course of a few years was highly appreciated by the Apostolic See and as a result, on 21st December 1923 by the bull "Romani Pontifices" of Pope Pius XI, the Syro-Malabar Hierarchy was established, raising Ernakulam to the status of a Metropolitan See and Trichur, Changanasserry and Kottayam as its suffragan Eparchies. Mar Francis Vazhappilly was the first Bishop of Trichur.
Mar George Alappat became the Bishop of Trichur in 1944. Pope Pius XII, by the bull "Saepe Fidelis" of April 29, 1955 extended the jurisdiction of the bishop of Trichur to the Civil District of Coimbatore. During the period of Mar Joseph Kundukulam, who is widely known as "the father of the poor', Trichur was divided to form two more eparchies. On June 20, 1974, Pope Paul VI by the bull "Apostolico Requirente" divided the Eparchy of Trichur erecting the Eparchy of Palakkad which consisted of the civil districts of Palakkad and Coimbatore. Again on June 22, 1978, Pope Paul VI separated the entire Taluk of Kodungalloor, greater Part of Mukundapuram and small portions of Paravoor and Aluva to the north of the river Chalakudy from the Eparchy of Trichur and erected the the Eparchy of Irinjalakuda by the Apostolic Bull "Trichuriensis Eparchiae".
Pope John Paul II inaugurated the centenary celebrations of the Eparchy of Trichur on 7th February, 1986 at St. Thomas Nagar, Trichur, in the presence of about one million people. On 20th May, 1987 the centenary day was celebrated. The concluding functions on 9th August 1987 were presided over by Simon Cardinal Lourdusamy, the then Prefect of the Congregation for the Eastern Churches. The eparchial renewal project - Evangelization Decade - was inaugurated on 30th December, 1990.
The long awaited expectation of the faithful of the Eparchy of Trichur was fulfilled on 18th May 1995 when the Pope John Paul II raised the Eparchy to the Metropolitan status with the Eparchies of Irinjalakuda and Palakkad as its suffragans. Mar Joseph Kundukulam was installed as the first Metropolitan Archbishop of Trichur.
Mar Joseph Kundukulam was succeeded by Mar Jacob Thoomkuzhy on 15th February 1997 who is leading the Archeparchy to its heights with projects and movements like Mary Matha Major Seminary, Jubilee Mission Medical College, Engineering College, Jeevan TV. On 19th March 2004 Mar Andrews Thazhath was nominated the first Auxiliary Bishop of Trichur. The Biennial General Assembly of the Catholic Bishops' Conference of India (CBCI) was held at Marymatha Major Seminary, Trichur, from 7 to 14 January 2004. 150 Bishops, the Prefect of the Congregation for the Oriental Churches, Rome [His Beatitude Ignace Cardinal Moussa I Daoud], the Apostolic Nuncio Archbishop Quintana and many other dignitaries participated. The public reception given to the Bishops on 11-1-2004 at Thope Stadium was the second historic event of Trichur after the Papal visit in 1986.
The present Arch eparchy of Trichur has the following boundaries - North : Bharathapuzha in Malappuram district, and Trichur - Palakkad district boundary; West : Arabian Sea; East : Trichur district boundary; South : Southern boundary of Valapad village and Karuvannur, Karanchira, Kurumali, Mupliyam river.