The First Parish Church dates back to the beginning of the town of Medfield in 1649, in which settlers from Dedham and Braintree, Mass. requested the incorporation of a new town by the General Court which was subsequently granted in May of 1651. They founded the Medfield Church of Christ in the same year, calling Rev. John Wilson as their first pastor.
The second minister was Rev. Joseph Baxter, a Harvard graduate and native of Braintree, Massachusetts, who served from 1697-1745. During his ministry the church membership grew from 65 to 375, and a second meeting house was constructed in 1706.
During the pastorate of the fourth minister Rev. Thomas Prentiss, which lasted from 1770-1814, a third meetinghouse was built, dating to 1789. As of 2019, a heavily remodeled version of this building is still standing, and is listed on the National Register of Historic Places. The specifications for the wooden frame of the building are given in detail in the town records and include details of the heavy timbers used in construction, which were hand hewn oak measuring 14 inches square. The building's tower was 52 feet high and surmounted by a belfry and cupola. In 1809 the inside of the church was refurbished, with seats in the body of the meeting house being taken up and replaced with pews, as well as the creation of a segregated gallery seating area for non-white parishioners.
In 1813 the town and the parish began to be legally separated. The members of the church incorporated as The First Parish. In 1816 the trustees of the Medfield Ministerial Fund, Inc. were granted a charter and by-laws by the General Court. The first Sunday school was organized in 1818, officiated entirely by women, with the wife of Rev. Thomas Prentiss playing an active role in its administration.
In 1827 a group of members of the First Parish petitioned for permission to withdraw from the First Parish, which was becoming increasingly Unitarian, in order to form an Orthodox church. An ecclesiastical council was called and granted their request. The Orthodox Church of Medfield was organized officially on February 6, 1828 with 17 total members, and is still active today as the United Church of Christ in Medfield.
The original First Parish church was subsequently known as the First Parish Unitarian church from 1828 onwards. The meeting house was extensively remodeled again in 1839, including a complete reorientation of the front of the building from east to south, and the construction of a larger spire. During the hurricane of 1938, the taller spire which had been added when the building was remodeled in 1839 was destroyed, and remains un-replaced.
By the 1970s the congregation had diminished to 10 members and was in danger of dissolution. Growth increased in the following decades, however, to the extent that the Unitarian Universalist Association granted the church an award in recognition of their revitalization. The church continues to serve the Medfield community today.