The school which metamorphosed into what is today known as St. Theresa's Grammar School dated far back to 1940s and 1950, when the quest for Primary Schools in Nigeria Delta area electrified the need for a Teacher Training College. Eventually, an Elementary Teacher Training College (ETTC) popularly known as MARYFIELD COLLEGE basically for girls was built in Ughelli in 1954. The girl's college was to train teachers for grade III and later grade II certificates. Attached to the then was a Demonstration Primary School under the management of the Sisters of Our Lady of Apostle (O.L.A), Congregation. Srs. Evaristus (Mary) Maddock, Canice Roche and Elfreda (Una) Downey were appointed Principal and teaching staff respectively. Initially, there was no staff house, so the Sisters lived in the O.L.A. Convent, Warri and drove out each day to teach classes and supervise boarding arrangements. The Elementary Teachers College was grant-aided in 1956 and when there were enough buildings, Srs Mary Maddock and Stella Marie O' Sullivan moved into the residence on the school premises and they tried to establish and maintain a standard, solid educational foundation. The O.L.A Sisters Congregation, who trained some Sisters of the field, left the system, handing over the administration of the college to the latter in 1958. The College was later upgraded to a Grade II Teacher Training College (TTC) with Mother Mary Michael Maxwell (EHJ) in charge.
Just as the Grade || College phased out, Mother Mary Michael Maxwell (EHJ) succeeded in obtaining permission to establish a secondary school in its place, and the proposed school which was eventually founded in 1966 in St. Theresa's Grammar School. She then requested that the OLA Congregation personnel take charge of the administration temporarily, since her congregation was yet to have equally qualified personnel for the position of a principal. In response to this, Sr. Theresa Hourigan (OLA) was transferred from Lagos and she lived with the EHJ Sisters. However, Miss Constellus, an Irish Peace Corps Member of the United State of America became the first Principal. The American Peace Corpers (A.P.C) were used by Nigerians at that time to teach in secondary schools. Working as a team with Rev. Mother Mary Michael Maxwell (EHJ) and Miss Constellus (A.P.C) in the new St. Theresa's Grammar School were Rev. Mother John Baptista (EHJ), Rev. Mother Catherine (EHJ), Miss McRich (A.P.C), Miss Willkinson Call (A.P.C), Chief M.S Oru, Rev. Mother Theresa Ebhodaghe (EHJ), Rev. Sr. Philomena Atsanbe (EHJ), Rev. Sr. Catherine Omaka (EHJ) and a host of others. However, in the early 1970s, during the military era, St. Theresa's Grammar School, Ughelli, was together with other mission schools, taken over by the Nigerian government. Worthy of note is that the school has produced eminent and well to do citizens in our society amongst who are; Dr. Mrs. Veronica Ogbuagu, an erstwhile Commissioner for Education in Delta State, Princess Oduaran Josephine, a post Local Government, Jeremi; Barrister Mrs. Awhotuyasere Mary, a serving commissioner in the Delta State Ministry of Commerce and industry among others. During the period when the government was in charge of its administration, the school was referred to by the Urhobo speaking people as OVIE R'EYA (Queen's Grammar School). Withing the period, some of the principals that worked in the school were Mrs. Akarainwe, Mrs. Obiazor, Mrs. Akpobome Oti Victoria, Mrs. Idiodemise, Mrs. Emumejaye and Mrs. Eyaruwe. In the year 2011, the Delta State Government under the Leadership of Dr. Emmanuel Eweta Uduaghan as the State Governor and professor Patrick Muoboghare Commissioner for Basic and Secondary Education, returned forty (40) mission schools, twenty-seven (27) of them belonging to the Catholic mission with St. Theresa's Grammar School as one of them. Meanwhile, before these school were returned, St. Theresa's Grammar School was together with other schools enlisted amongst schools to be rebuilt by the Delta State Government. At the moment, the project, a two- storey building which is almost completed contains about twenty-four (24) classrooms, Laboratories, offices, staff rooms, library, sport facilities, two (2) modern and standard hostel blocks with common room etc. The school was returned to the Catholic Diocese of Warri under the leadership of Most Rev. Dr. John Okeoghene Afereha who, immediately, contacted the Congregation of the Sisters of the Eucharistic Heart of Jesus (EHJ) for the management of the schools since they were the original initiator of the school, and have been in the management of the school before the government took over. The school started full academic operations on the 12th of September, 2012 with Rev. Sr. Clementine Ekere (EHJ) as the first principal. She was assisted by Rev. Cecilia Omoogun (EHJ), seven (7) regular academic staff, two (2) part time academic staff four (4) non-academic staff and forty-one (41) students. The State Ministry of Basic and Secondary Education staff, Asaba visited the school to access the extent of compliance to minimum standards in the school on Monday, 6th February, 2013. Rev. Sr. Ocloo Theresa Omolara (EHJ) resumed office on the 5th of February, 2015, as the second principal of the school. Rev. Sr. Catherine Oparaji, later joined the school on the 4th of January, 2016, Also, Rev. Sr. Anki Patricia - Marie Inyang was transferred to the school on October 14th, 2019. The school wrote the first external examination (WAEC & NECO 2017/2018) with a total number of 21 students after the returns of school back to the missions and to the glory of God, the track of performance recorded was 100%.