Saint Nicholas' Chapel is a Chapel of Ease to St Margaret's church (King's Lynn Minster) and was founded in 1146. The Chapel consists of a south west tower with spire, nave and clerestory continuous with chancel, south porch, and vestries. The tower is from the 13th century, and was subject to settling due to the soft ground. The church was enlarged in the late 14th century to create the largest Chapel of Ease in England. It is some 58 m long and 22 m wide. The nave has an 11 Bay arcade with north and south aisles and clerestory. The nave roof has carved Angels playing musical instruments placed on small hammer beams above the clerestory windows. There is a two-storey south porch, the lower level has a lierne vault with carved bosses. The chancel has the mutilated remains of a sedilia on the south wall, which once would have been very fine. It is unknown why it was mutilated. In the north-west corner of the nave survives the Consistory Court which dates from the early 17th century, where people were tried for various moral matters.

By the early 19th century the church was full of galleries and pews which belonged to properties in the town, some were even let out for cash, only under half were free. These were swept away in the mid 19th century, unfortunately this also included mediaeval woodwork, although some still remains in the stalls.

In 1741 the existing spire of the church, dating from around 1500, blew down in a gale. The spire was replaced, but this was unsatisfactory, and the present lead-covered spire, designed by George Gilbert Scott was completed in 1869.

In the 20th century due to declining numbers, the church was declared redundant and now in the care of the Churches Conservation Trust since 1992.

There are several fine monuments at the east end of the chancel.