Holy Trinity is England's largest parish church (by area), and was founded in 1285. It did not become a parish church until 1661. The church was restored in 1841 by H. F. Lockwood, and from 1859 to 1872 by G. G. Scott.

The church consists of a nave and chancel, both with aisles, transepts, crossing tower, south porch, south Chapel, and vestries. The nave has clerestory windows. It is cruciform in shape with short transepts. These were built first circa 1300, followed by the chancel, and nave some hundred years later. The tower dates from circa 1500.

The church is built in ashlar and brick (one of the earliest examples in England) with lead roofs. The original lead roofs were extremely thick and heavy, and had to be replaced as they were causing subsidence of the structure. Externally, the church has buttresses, battlemented parapets and crocketted pinnacles, the nave having mostly five light windows, many of which have clear glass.

The crossing tower is of two stages and is topped with pinnacles, with an open work parapet. On each side there is a skeleton clock dial, the largest four faced church clock in Britain, with each face 4m in diameter. There are 15 bells. The organ is in two cases located under the crossing tower.

The choir has five-bay arcades with a seven light east window by Clayton and Bell. The east end has a stone reredos from 1886, and the roof has painted panels and bosses. To the south of the choir is the Broadly Chapel, formerly the De la Pole Chapel which is the only remaining Chantry Chapel of an original twelve in the church.

The nave has eight bay arcades with slender piers consisting of four round shafts with hollows between them. The clerestory has 16 triple lancets and there is a 19th-century west stained glass window of nine lights. The interior of the church is very long at 285 feet.

In the early 19th century due to growing congregations a gallery was built across the west end. This was removed in the 1840s, when the pews with poppy heads were introduced. They have a range of carvings by local craftsman George Peck.

The font dates from circa 1380 with very fine carvings.

There are many memorials in the church dating from the late 14th century onwards including a brass from 1451. There is an effigy to Sir William de la Pole and his wife from the late 14th century.

The organ is by Forster and Andrews, incorporating pipes by Snezler. Unfortunately at the time of writing, it is in poor condition. (Mid 2016)

There are two south aisle stained glass windows designed by Walter Crane, good examples of early Arts & Crafts work.