Summerside Trinity United Church has its origins in three separate groups within the Summerside, Prince Edward Island, community. One of its ancestral partners, the Wesleyan Methodists, began to hold religious services in 1850 at what was then called Green's Shore, now Summerside. At that time there was no church in the community so they held their services in the district schoolhouse. Mr. and Mrs. Joseph Green donated property on First Street in 1853 for the purposes of building a church. The building was completed in 1860 and was formally dedicated by Rev. John B. Strong and Rev. Ingram Sutcliffe.

In 1870, the Bible Christians, who had been worshiping with the Methodists, decided to build a hall on Spring Street for their own religious services. A new church was completed in 1874 and the former hall was used as a vestry. The Bible Christian Minister, Rev. J. A. Dafoe, remained until 1883 when the Bible Christian Church united with the Methodist Church of Canada. Worship was held in the church belonging to the Methodists while the Bible Christian's former church was sold and became part of St. Paul's Hall.

In 1893, a piece of land was purchased on Spring Street and the church which was erected there became the Methodists' new home. The cornerstone of the new church was laid by Honorable W. G. Strong. Special trains came from all over the Island, bringing crowds to Summerside to witness the ceremony. When church union was voted on in 1925, one hundred members, five of them elders, came from the Presbyterian congregation to form Trinity United.

Renovations in the chruch basement in 1947 provided a central auditorium surrounded by nineteen Sunday School classrooms. In May 1957, construction began on an extension of the building. The congregation worshiped in the Civic Auditorium and Epworth Hall until the renovations where complete. On 17 November 1957, Rev. C. R. Webber reopened and dedicated the renovated and enlarged Trinity United Church.

The congregation at Trinity United continued to grow and in 1958 a call was extended to Rev. A. S. Weir, D.D., who became the first Minister of Visitation. A call was also given to Rev. G. C. Wells to become the first Associate Pastor.