[1] Much of the present building was erected in 1412 by Thomas Langley (born in Middleton in 1363) who was Bishop of Durham and Lord Chancellor of England.

The church of St Leonard was enlarged in 1524 by Sir Richard Assheton, in celebration of the knighthood granted to him by Henry VIII of England for his part in the Battle of Flodden in 1513.

The Flodden Window, in the sanctuary, is thought to be the oldest war memorial in the UK.

The church also has one of the finest collections of monumental brasses in the north of England, including the only brass in the UK depicting an English Civil War officer in full armour, Major-General Ralph Assheton.

George Pace designed a war memorial and, in 1958, added a choir vestry and installed new lighting.