In May 1872, the Bangor Congregation of St. John's Church was divided and a new parish was formed. The Rev. John W. Murphy was appointed pastor of St. Mary's parish, originally built on Cedar Street. The parish included the area of Bangor west of the Kenduskeag Stream, Hampden, Hermon, and Carmel. While St. Mary's was in the early stages of construction, Father Murphy engaged the auditorium of Bangor City Hall as a place of worship. When the church basement was completed, a temporary altar and seating were set up for Mass. The cornerstone of St. Mary's was laid in September 15, 1872 by Right Reverend D.W. Bacon, Bishop of Portland. The church was dedicated on December 8, 1872, by Right Reverend Bishop Lynch of Charleston, S.C.

Father Michael C. O'Brien succeeded Father Murphy in 1880. During his 21 years of pastorate, Fr. O'Brien built the rectory, installed the organ and built a school. During the years 1908-1933, stained glass windows were installed and a bell was installed in the tower.

Beginning in 1967, a major restoration was begun on St. Mary's. In 1972, the 100th Anniversary of St. Mary's was celebrated. In January of 1977, a fire extensively damaged the rectory. It took firefighters almost 6 hours
to extinguish the blaze. But that fire was a mere foreshadowing of what would come a year later.

On February 3, 1978, in sub-zero temperatures, a young man set the fire that would destroy St. Mary's Church, a 105-year-old landmark. Remembered as one of the worst fires in the city's history, it would change the lives of many Bangor Catholics forever. Unharmed by the fire were the crucifix, the nave, the altar, sacred vessels, and a few of the stained glass windows. The pews were covered in a thick sheet of ice. The next day, Mass was held at the Bangor Auditorium, where a huge crowd gathered and the healing began.

On September 9, 1979, groundbreaking was held for the new St. Mary's Church on Ohio Street. Masses were celebrated at Dow Field during the construction of the new church. St. Mary's architecture is distinctly modern. The primary design captures the unmistakable lines of a tent (the hallmark of the ancient desert-dwelling nomads of the Holy Land).

On October 31, 1980, the first Mass was celebrated on the Vigil of All Saints. On December 14, 1980, Bishop Edward C. O'Leary dedicated the new church at an Ecumenical Service.

Today, the original St. Mary's crucifix hangs above the altar and the tower outside the main entrance supports the bell taken from the original St. Mary's steeple. Restored stained glass windows are installed in the chapel and sanctuary, as well as the parish office at St. John's Church.