Although no documentary evidence of the foundation of the church appears to be in existence, there is some evidence that there could well have been a place of Christian worship at Horfield from a very early date.  Until the building of the school in 1838 (for which authority to enclose part of the common was granted) the churchyard was completely circular in form.  This, together with the many springs still in evidence, suggests that the site was originally a pre-Christian place of worship.  Moreover, it is adjacent to an exceedingly ancient track-way leading from Bristol towards the crossing of the Severn at Aust, part of which is currently in use as a short cut between Wellington Hill and Kellaway avenue past the east end of the church.  This track can be followed on foot back to Zetland Road and from there over Kingsdown to the old city.  It is not beyond the bounds of possibility that this track was the route followed by St. Augustine to the conference with the Celtic bishops at Aust in 603 AD.  As Augustine was ordered by Pope Gregory to re-dedicate existing places of worship to Christian use so that converts could continue to worship at a place to which they were accustomed, it is possible that the foundation of the church in Horfield dates from this time.

Horfield appears in the Domesday Book as 'Horfelle in Langlei Hundred, the property of the King in Horfelle VII hides'.  The book was compiled principally to record the extent, value and ownership of the lands, therefore the omission of a direct reference to an actual church building by no means precludes its existence.  In any case it would probably have been quite small and built of wood or wattle.

The Manor of Horfield formed part of the estate given to Robert Fitz-Harding by Henry I (1100-1135) and when Robert established his new Monastery of St. Augustine in 1140 it formed part of the endowment, together with the advowson (the right to appoint the Incumbent) which clearly points to there already being a well-established church in existence by this date.

No doubt the Abbot of St. Augustine shortly re-built the church in the Early English style (1175-1275 approx.) as an updated sketch, probably early 19th century, shows a small building comprising a nave, chancel and south porch attached to the later tower, with double lancet east windows typical of this period.  Unfortunately, nothing remains of this church except the capital of a pillar now displayed in the church.

The present church dates from 1831, when The Revd. Henry Richards (who succeeded the Revd. Samuel Seyer in 1828) found that the old building was much too small to accommodate the increasing number of parishioners and after raising some £500 by subscription he contracted with 'Masons, Carpenters and Plasterers' to undertake the enlargement.  The unknown architect engaged found upon commencement of the work that the whole of the fabric, with the exception of the tower, was in such a dilapidated state that it was necessary to completely demolish and rebuild the roof, nave and chancel.  The tower is 15th century and it is interesting to see the date 1612 cared into the south west buttress, proving that this practice is nothing new!

The new church consisted of nave, chancel and transepts, with galleries in both transepts and across the west end extending into the tower.  The former south porch was not replaced, an entrance being formed through the tower.  Unfortunately, no faculty was obtained to carry out the work.  This no doubt came to light when the Sees of Bristol and Gloucester were united in 1835 and a petition to rectify the oversight was hurriedly presented to Bishop Monk on the 14th December 1836.  The total length of the new nave and chancel was 61 feet 5 inches with a width of 16 feet 3 inches, these being the dimension of the mediaeval church, the transepts projecting 12 feet from the nave with a width of 16 feet.

Further building developments in the parish, which was very much larger than it is today, together with the decision to build an army barracks in Horfield led to the question of further enlargement.  This time a faculty was sought.  It was granted on 17th October 1846.  Building commenced the following year under the supervision of the architect William Butterfield, who was becoming known locally through his work at Highbury Chapel (now St. Mary's) Cotham and at Coalpit Heath.  First the galleries were removed, and the chancel extended.  Services were held in the new chancel whilst the north and south aisles were formed by extending the transepts back as far as the tower.  The nave was 48 feet long and the chancel 24 feet 6 inches with an overall width of 40 feet.  The completed church was consecrated on 22nd December 1847.  A white marble slab with a black cross marks the site of the 1847 altar.  The choir vestry at the west end was built in 1887 to commemorate Queen Victoria's Jubilee.

In 1893 the church was considerably enlarged by removing the chancel and rebuilding it on a larger scale eastwards of a high central lantern tower, together with a Lady Chapel and short transepts.  The south transept was completed with an eastern door and porch in 1913 and the north transept was constructed to include a sacristy with organ chamber over it in 1927.  This constituted the church as we see it today, with the exception of the removal of the chancel screen, the repositioning of the font to the south transept and the formation of St. Edmund's chapel.  The Stations of the Cross were originally in St. Edmund's church. 

The organ, built in 1885 by Palmer of Kings Square, Bristol, was originally situated in the north chancel aisle. In 1927, it was moved to a purpose-built chamber above the new Sacristy with a detached console in the choir. It remained in this state until 1973, when Percy Daniel of Clevedon electrified the action and carried out numerous tonal modifications. At some stage, a fine tuba stop was removed – one can only assume that it was too loud for our small church! By 1994, the organ was in desperate need of a major overhaul and, following the receipt of a generous legacy, this work was very ably carried out by E. A. Cawston; weaknesses in the action were addressed and several new stops added, including a number of mutations and a Great Trumpet. In 2015, a new solid-state action was installed by Nicholsons of Worcester, and the opportunity was taken to revoice the Trumpet (now playable on both the Swell and Great), to add a sub-octave coupler on the Swell and to stabilise the winding system. The result is a fine and versatile instrument, ideally suited to the needs of the church.

The earliest church registers, dating back to 1543, have been deposited at the Bristol Records Office where they can be viewed on request.

Horfield's belfry is the smallest in Bristol, being only nine feet square and is almost unique in having five bells.  The four largest bells, dated 1773, were cast by Bilbie of Chew Stoke.  The treble was cast by Rudhall of Gloucester in 1807.  In 1982 the bells were recast and re-hung on oak wheels in a new metal frame.  The original 4th was broken in 1997 and was replaced the following year by a similar bell which originally hung at South Petherton in Somerset.

There is a comprehensive collection of Communion Plate, but nothing is earlier than 1847.

Some monuments have been preserved from the old Church and have been placed on the walls of the nave and chancel aisle.  They include some to the Shadwell family, who were 'Lords Farmer' of the Manor and one of interest, just behind the organ console, is to George Armstrong, who fell into the River Frome near the drawbridge and was drowned in 1799. The font is original and could be contemporary with the tower.  The eagle lectern, a gift from the Revd. Fanshaw Bingham (Rector 1878-1899 and author of a useful history of the parish) was stolen in June 2002.  The stained glass in the aisle was given by the Richards family in memory of their deceased children, whilst the East window is a memorial to the wife of one of the Rectors, The Revd. Clement Hutchinson.  In the Lady Chapel the east window is dedicated to Archibald Walters, known as 'The Boy Hero', who died from exposure in a field in the parish in 1874.

The dedication of the church is to 'The Holy Trinity with St. Andrew'.  A further dedication to St. Edmund was added to commemorate the redundant daughter church on Gloucester Road (1905-1978).  Built in 1860, this was originally one of the parish schools.  It has since been demolished.  Holy Trinity was apparently not the original dedication - a Bristol will of 1502 refers to 'The Church of St. Andrew in Horfelle' and this was also the dedication of the churches of Cromhall, Ashleworth and probably Alveston, all of which formed part of Fitz-Harding's original endowment.  The See of Bristol was formed in 1542 when the Abbey Church of St. Augustine became the Cathedral - dedicated to 'The Most Holy and Undivided Trinity'.   As the Manor of Horfield now formed part of the endowment of the new Diocese, it could be that the same re-dedication was given to the Parish.

There is no record of how the church was served by clergy prior to the foundation of the Abbey, but from then until the Reformation it was doubtless served by priests appointed by the Abbot.  From various sources it appears that Horfield was somehow annexed as a curacy of Almondsbury and it was not until 1813 that the first permanent Incumbent was appointed.  This was the Revd. Samuel Seyer, known for his History of Bristol, who served as perpetual curate.  He was responsible for the building of the Georgian Parsonage, completed in 1825, although he himself never resided there.  Horfield was not created a Rectory until 18th June, 1867, when The Revd. H. H. Hardy became the first Rector.

Horfield was at the forefront of the Oxford Movement in the area, as is clearly evidenced by press reports in the local newspapers of the opening of the new chancel in February 1847.  All the key figures of the movement, such as the Revds. Eland, Woodford and Prevost took part in the service and on the following Sunday the preacher was none other than Dr. Pusey.  The actual pulpit from which he preached was erected in St. Edmund's, but unfortunately the Jacobean woodwork literally crumbled to pieces when the church fixtures were dismantled.                                                                                                                                                                                                      (Revised 2018)