The town was first mentioned in the Domesday Book of 1086 as Neuport, which is Old English meaning New Market Town. At that time it was fairly new, having been founded by Norman invaders. The suffixe Pagnell came later, when the manor passed into the hands of the Pagnell (Paynel) family.
At one time Newport Pagnell was one of the largest towns in the County of Buckinghamshire (the assizes of the County were occasionally held here), though today it has been completely dwarfed by the growth of Milton Keynes. The two have joined up and there is no easy distinction to see where Newport Pagnell ends, and Milton Keynes begins.
The position of the old castle that was the home of the Pagnell family is where Castle Street is today, though no part of the castle remains. There were also at one time two hospitals in Newport Pagnell and six fairs were held for the townsfolk throughout the year.