This is a large, cruciform, fenland church with central tower and spire. Between 1850-54 R.C. Carpenter carried out a major restoration on the entire church under the direction of the then rector, Rev. Basil Beridge. Five-bay nave arcade, transepts, tower, and chancel date from the 13thc., the clerestory was added in the late 15thc. and the spire was added in the 19thc.; the large 14thc. E and W windows, N and S transept windows, and the chancel were renovated in the 19thc. as well. The transepts are unusual in being double-aisled. Romanesque remains consist of the capitals of the W crossing piers, the W arcade respond capitals of both the N and S transept as well as a label stop on this arcade, and a respond capital of the arch leading into the N transept, E chapel.

Though Algarkirk is cited in the Domesday Survey as 'Alfgare', there is no mention of a church here in 1086. The lack of the suffix 'kirk' in the Domesday Survey suggests that it was post-1086 when a church of such consequence, perhaps being in stone, was constructed and so led to the name change.

The two-step, plain arcade arches, keeled shafts and necking, and the use of early stiff-leaf in the same context as waterleaf capitals suggests a late 12thc. date for the Romanesque material here. Another possibility, however, is the presence of experienced sculptors in the early 13thc. workshop responsible for the nave arcades; sculptors who brought with them a tradition of earlier forms and motifs.