St Mary's Church has developed over the years from an original small Norman building on the site dating from the 12th century. It is quite possible, however, that an earlier Saxon church may have stood on or near the site of the current church. The earliest parts of the interior of the existing church are built with malm stone, perhaps from the Perryland quarry a mile away.

Early authorities give 1170 as the date of the Norman pillars on the north side of the Chancel, 1180 and 1240 respectively for the North and South Chapels and 1190 for the Low Tower. More recent surveys suggest that the North Chapel, now the Vestry, and the Norman arcade with its scalloped capitals, were added about 1200 and the South Chapel in the late 13th century. Traces of medieval colour ("scroll" work and "English" roses) are still visible in the Chancel. The present east window replaced the original Norman work. Most of the glass is Victorian, but the two lights immediately below the quatrefoil at the top are original. There is also 15th century glass in one of the clerestory windows.

Bentley Parish Church has a ring of six bells, the Tenor weighing just under 13 hundredweight (about 660 Kilos). The earliest bells date from 1703 but some were recast by Gillet & Johnson in 1912.

The Font basin is at least as old as the church. It was found a century ago in a nearby farmyard. It is now in its original position but on a Victorian base. behind the Font is the great Early English arch opening into the Tower.

When the South Chapel, now St. Martin's chapel, was added, a second arcade of taller, two centred arches was built. All these pillars have "consecration crosses" incised on them - large circles, each enclosing a Maltese Cross. These were probably placed here in 1400 when William of Wykeham authorised one of his Suffragan Bishops "to dedicate the Chancel of the Parish Church of Bentley and the High Altar which has recently been built and the other Altars if necessary". This suggests a restoration after the neglect and decay such as followed the Black Death of 1348-49.

On some of the pillars small "pilgrim" crosses have been scratched in the stone, perhaps by those Canterbury pilgrims who came through Bentley on their way to the shrine of St. Thomas à Becket.

The Organ was built to commemorate the Jubilee of Queen Victoria in 1897 by the firm of William Hill & Son and was further extended in 1968 and 1993.

Not pictured here is an acient chest located on the north wall of the Nave made in about 1540 to house the Parish registers. These registers go back without a break to 1538, the year Henry VIII required all parishes to keep them.

On leaving the church it is worthwhile for visitors crane their necks a little and look at the roffs of the Nave and St. Martin's Chapel. For many years these were ceilinged over but the timbers now exposed are, in the main, those used in the restoration of 1400.