There has been a church on the site for about 1,000 years. The present church was consecrated in 1747 and extended westwards in 1844 and again in 1878 to include a new chancel and sanctuary, the side chapel being consecrated in 1912. St John-at-Hampstead is within the Diocese of London and the Province of Canterbury. It is part of the world-wide Anglican Communion.
The legal responsibilities for the maintenance of the building and, when they applied, the collection of pew rents, were reconstituted by a private Act of Parliament of 1827 which provides for the election by the Vestry of a body of Trustees. Such Trustees are still elected, though their functions were somewhat overshadowed by the establishment of Parochial Church Councils in 1921. Members of the Council are elected at the Annual Parochial Church Meeting not later than 30th April in each year by parishioners whose names are entered on the Church Electoral Roll of the parish. Members of the Deanery Synod are elected at the same meeting every third year and they themselves form an electoral college for the elections to the Area, Diocesan and General Synod under the Synodical Government Measure 1969. Each member of Synod is an ex-officio member of each lower synod for his or her own locality and also of the Council for his or her own parish.
The offices of Churchwarden and Sidesmen are of ancient origin, though their annual election is now governed by modern legislation. Sidesmen are elected by the Annual Parochial Church Meeting and Churchwardens by a wider body. Churchwardens, with the Vicar, are ex-officio members of the Council, ex-officio Trustees, ex-officio Trustees of the Hampstead Parochial School and ex-officio Trustees of the Additional Burial Ground under a private Act of Parliament of 1810.
Meetings of the Council in this parish are held regularly, about five a year, and between meetings the business of the council is conducted by the Standing Committee of which the Vicar and Churchwardens are ex-officio members and other members are elected.