Catholicos Baselius Thomas I was born in the Cheruvillil family of Vadayambadi Puthenkurishu to Mathai and Kunjamma on July 22, 1929. As a child, a stray dog bit Thomas frightening the little boy. Subsequently he had frequent bouts of illness which affected his education. His mother used to take the young boy frequently to the nearby Malekurishu Dayro where the relics of late Patriarch St. Elias III had been interred. One night, as his mother prayed with the young boy on her lap, she had a vision which prompted her to dedicate the boy to the service of the church. Within days, the boy's illness was entirely cured. His priestly formation was under the guidance of Mor Philoxenos Paulos (later Catholicos Paulos II) who ordained him korooyo in 1952 and shamshono at Kadamattom Church in 1957. In 1958, he was ordained priest by Mor Yulius Elias Qoro in September 1958 at Manjinikkara. He was the 43rd priest from the Cheruvillil family. Fr. C.M. Thomas served as the vicar of St. Peter's church, Puthenkurishu from 1959 while also serving churches at Vellathooval, Keezhumuri, Fort Cochin, Valamboor and later at Calcutta and Trichur. In 1960, while vicar at Puthenkurish, he played a key role in rebuilding the church; parishioners fondly recollect their priest working with them during the reconstruction. From 1967-74, he served as the organizing secretary of Kolenchery Medical Mission Hospital. In 1970, he served as the organizer for the North Indian mission at Bhilai and in 1974 as the secretary of the Pourasthaya Suvishesha Samajam. Since his ordination as korooyo, at age 24, Thomas was active in preaching the gospel in the remote parts of Kerala. From his vision and zeal to spread the gospel arose the St. Paul's prayer fellowship and the Puthenkurish gospel convention which is held annually from December 26-31.
Fr. Thomas was elected to the episcopate by the Malankara Jacobite Syrian Christian Association meeting at Karingachira St. George Church in January 1974 and was consecrated metropolitan of the Ankamaly diocese, the largest Syriac Orthodox diocese, by H.H. Mor Ignatius Ya`qub III on February 24, 1974 at Damascus along with Mor Gregorius Gheevarghese. The two metropolitans played a significant role in leading the church during the crisis of the seventies. After the passing away of late Mor Gregorius Gheevarghese in February 1999 , Mor Dionysius assumed the Presidency of the Malankara Syrian Orthodox Church Synod (Patriarch Faction) and was elected Catholicose-Designate at the delegates meeting held at Puthenkurishu on December 27, 2000 and again by the Malankara Association reconstituted under the newly formed constitution on June 6, 2002. On July 26, 2002, Mor Dionysius was consecrated Catholicos by H.H. Patriarch Mor Ignatius Zakka I Iwas at Ma`rat Sayyidnaya, Damascus.
• Malankara Shabdam (1974 January 30), p.1 quoted in Moolayil, Very Rev. Kuriakose, Perumpilly Thirumeni: Malankara Sabhayude Kal Noottandu, 2001.
• Malayalam dailies published on June 27, 2002.