Rev Fr Mathew Olassayil was the third son of Late O. V. Thomas and Late Elykutty.

He joined seminary on 8^th December 1979 and ordained on 6^th January 1980. He started his priestly career in 1^st February 1980 at St. John The Baptist Church, Eravipuram. He became Work Director at the Community Centre, Eravipuram and then the Vicar. He was raised to the level of Superior in Quilon Norbertine. In 1987 he was appointed as Trichy Norbertine Community Procurator with added responsibility at All Saints Church, Trichy. In 1922 he became Provisor in Indian Norbertine Priory, Jabalpur and thereafter in 1996 he served in Varnasi Catholic Mission. In 2001 he joined John Paul II Pontifical Institute, Thuruthy for Family Apostolate and Councilling Course.

In 2004 he was transferred to Jabalpur where he was teaching the aspirants, postulants and Novices at St. Norbert Abbey, Jabalpur. By mid of 2005 he was again transferred to Mumbai and was working as professional Counselor, at a Counselling Centre, named Kripa Foundation, Vasai, under the Archdiocese of Mumbai. He worked there till 2012 where he was down with Rheumatoid Arthritis. Because of this aliment it was impossible for him to continue in Mumbai and at his request, the Superior shifted him from there to Alwaye, Kerala for treatment. He was there in an Orphanage, run by one of the Norbertine priests. He had treatment there and was helping the students and the priest as well. His health got bit recouped and was transferred to St. Norbert Minor Seminary at Ayathil, Quilon where he was teaching the seminarians and was helping at St. John the Baptist Church at Eravipuram. Then he was appointed as the vicar of Viswa Rani Church at Ayathil, Quilon on August 10, 2015. Following severe sickness he was hospitalised and then was taking rest in Quilon. His health condtion deteriorated and was called by God Almighty  for eternal rest on 11 April 2019. He was the Patron of Kudumba Sanghadana