The bridge is built of coursed limestone rubble and is held to date from the 14th century, though with many later repairs. Indeed, as will be seen below, the history of the bridge is one of continuous repairs.

Six arches, covering 213 ft (65 m), span the River Great Ouse and are known as The Great River Bridge. There is a 49 ft (15 m) causeway for traffic on the south side then nine flood arches cross the fields for another 197 ft (60 m). South of the road bridge a foot causeway crosses another 650 ft. (198 m) of field, which regularly floods, parallel to the modern road to Carlton. The bridge is quite narrow and traffic only flows over it one way at a time, governed by a set of traffic lights. The parish boundary with Carlton lies directly south of the bridge.

The first mention of the bridge in history is in the period 1136 to 1146. A number of early 16th century wills made bequests for the upkeep of the bridge such as Thomas Russell of Stevington in 1509 who left two bushels of barley and Richard Rabett of Podington in 1511 who left a half quarter of barley. The first mention of repairs is in a bailiff's account of 1532-1533 in which arch number two, the responsibility of the Earls of Kent, was repaired.

From then on repairs dominate the references: in 1844 liability for repair was quoted in a document dated 1630 to lie as follows: Harrold Bridge 4 High Arches, the first Sir Richard Chetwode, the second the Earl of Kent the third and fourth the Lord Mordaunt. The 31 arches on the Long Bridge were the responsibility of the County

In 1651 a presentment was made at Quarter Sessions that the bridge was out of repair. In 1667 the Dowager Countess of Peterborough ( successor to Lord Mordaunt) was ordered to repair the third and fourth arches by the Assizes.

In 1694 it was again presented at the Assize that the bridge was out of repair and that the Earl of Peterborough, Edward Reynolds (Lord of the Manor of Carlton) and Charles Cutts (Lord of the Manor of Carlton Stayesmore) were partially responsible for repair.

A letter of 14th February 1795 reported that melting ice and snow had resulted in a flood which had rendered Harrold Bridge impassable and had swept that at Emberton [Buckinghamshire] away. The bridge at Harrold was damaged by a flood in 1824 and the county maintained part was repaired the next year, after an indictment at Quarter Sessions noted that it was unsafe.

In 1825 it was reported that: "Harrold Bridge was and yet is in a ruinous, broken and dangerous" condition". It was reported at Quarter Sessions in 1835 that the second arch was "much out of repair".

It was not until 1st November 1930 that the Highways & Bridge Committee of Bedfordshire County Council resolved that they would take over maintenance of the whole bridge. Harrold Parish Council records show further major repairs between 1986 and 1992. And Harrold Bridge was again being repaired in 2008.