The church consists of a nave and chancel, north and south aisles, west tower, vestry to the north and a south porch. However the main entrance is now through a suite of church rooms and chapter house built in the 1970s adjoining the northwest corner of the church.
The southwest window in the south aisle commemorates the Biggleswade fire of 1785 which destroyed a large part of the town. It was donated by Percy Moffat in memory of his wife in 1951.
The south porch has two storeys with the upper storey reached from inside the church. There is a window to the west and what appears to have been a similar window to the east which has been broken through to form an entrance to the east.
The original tower was rebuilt in 1720 and is of ashlar in contrast to the ironstone of the church itself.
There is a stair turret in the northeast corner of the tower built from ironstone so may be of a similar age to the original tower pre 1720. The tower contains a peal of five bells dating from 1721 and 1806.
The chancel contains a piscina now used as a credence and sedilia for three priests. The altar piece depicting the Last Supper dates from 1865 with the reredos behind dating from 1877.
The font has a plain bowl set on an octagonal panelled stem containing carvings of emblems of the crucifixion. The roof supports in the nave have an extensive collection of carved angels.