Didcot is a very ancient settlement which has been occupied since at least the early Iron Age. There may have been a Romano-British village just east of the parish church where pottery, jewelry, coins, a Roman coffin and possible foundations have been discovered. There were also two Roman villas in the local area. Most prominent, however, has been the finding of the 'Didcot Hoard,' a pot full of gold Roman coins dating from AD 54 to 160. They may have been a free gift, known as an 'accession donative', given to a member of the civilian or military administration when Antoninus Pius became Emperor. The coins can be seen in the British Museum.

The Saxons arrived in this area at an early date and a man named Wigbald apparently settled at Didcot with his followers. The place became known as Wibaldinton or 'Wigbald's people's town (ie. farm)' and Didcot retained this name until the 1150s. The old village is still very clearly defined around Manor, Foxhall and Lydalls' Roads. Didcot is a Saxon name too, traditionally associated with King Didan of Upper Wessex, the father of St. Frideswide. The name means 'Didan's Cottage,' presumably a retreat away from his main power base. Perhaps it was the name of the manor house, while Wibaldinton was the village. The name appears to have changed because the D'Albini lords of the manor held a second Wibaldinton (now Wyboston) in Bedfordshire.

Robert D'Albini gave up Didcot Manor to King Henry II as an apology for hitting him with a stone during the Siege of Bedford Castle, when Henry was fighting for his mother's throne against her cousin, King Stephen. There is said to have been some fighting in Didcot itself. Henry gave the manor to Hugh de Mara, whose other main home was at Kingston in Oxfordshire. The manor was closely associated with the Honour of Wallingford and the De Maras had to pay for or provide half a knight's service or two mounted sergeants-at-arms to defend the castle. Hugh's son, Geoffrey, was involved in a long court case with his neighbour at Kingston and, though he won, had to mortgage Didcot to Bonchose the Jew (from Oxford) to cover his costs. He paid the fine for his knight's service, but his son, another Hugh, sent a knight with horses and arms to Wallingford during the Baronial Wars in 1216.

Hugh Junior's daughter and heiress, Eleanor, married into trade, which was not popular with her mother. Her new husband, Andrew le Blunt , was a rich London merchant to whom Hugh probably owned money after his involvement in a prolonged court case with Tutbury Priory over the advowson (right to appoint rectors)  of Didcot Church. He had worked with his uncle, the Archbishop of Dublin, in Ireland and owned a number of other manors in Staffordshire and Essex. He seems to have been very careful with his money and managed to avoid the expenses of being a knight until just before his death in 1259. In order to continue to provide her knight's service, Eleanor needed to remarry, something she did without Royal permission in 1261. Her new husband was David de Uffington, a servant of the Bishop of London. Along with his step-son, Robert le Blunt, he became a follower of Simon de Montfort during the Baronial War of 1262-7. He was sent by him as an envoy to the King of Scots but, after Henry III's victory at the Battle of Evesham, he had to flee into the forest as an outlaw - but not before he had raided Didcot and taken away animals worth 10 marks (£6-13s-4d). He lived a Robin Hood-type life in Epping and other forests of the home counties until pardoned in 1267. From about 1270, Robert's brother, (eventually Sir) Hugh le Blunt lived at Didcot Manor, although he moved about between his other estates too. He did his military service during Edward I's conquest of Wales (1277) and his expedition to Scotland (1297), as well as Edward II's Scottish Invasion of 1314, when he was seventy. His son may have been killed at the Battle of Bannockburn.

In 1317, Didcot Manor was sold up to the Stonor family of Stonor Park, near Henley, in Oxfordshire. They didn't live in Didcot but employed stewards to run the estate. The first of these were members of the De Didcot family who owned an important farm in the village, hence their name. One of their number was Ralph de Didcot, Abbot of Dorchester, whose broken effigy was dug up in 1775 and restored to Didcot Church. Another important family in the parish were the Brunces from Harwell and Sutton Courtenay.

At the time of the Domesday Survey (1086), Didcot consisted of a church and twelve homes (housing perhaps seventy people). By 1438, there were thirty-nine adult males (perhaps 120 people), a figure that was pretty constant until the early 18th century, although had dropped from the previous century, probably due to the Black Death. The villagers farmed the open field system, mostly growing barley and raising sheep. The common grazing land was at 'the Marsh,' north-east of the village. It was only finally enclosed in 1852. Villagers' grain was ground in a windmill that stood on Windmill Hill just west of the village. Some of the cottages still standing in Didcot date from the 15th century. Many more were built in the following two centuries. The early 16th century thatched Rectory Cottages was the old manor  or 'mansion' house. It was the village school in 1854, but was previously called 'Lydalls' after the family of that name who moved there from Ipsden in Oxfordshire in 1654. But they only stayed until 1742. Other important families around this time included the Blakes of Manor Farm and the widespread Sawyers.

In the early 1600s, Richard Sawyer mortgaged his copyhold estate in Didcot to Sir Francis Stonor for £120 under a ten year repayment programme. Sir Francis let him stay on his farm, but Richard quickly fell into arrears and, in 1621, he was arrested and thrown into prison in Reading or Abingdon. He was later released but, the following year, another warrant was issued for his arrest as he also owed money to the Blake family. Officials arrived in Didcot from the Fleet Prison in London to arrest Richard, but he shut himself up in his house and threatened to kill anyone who helped them. A large crowd gathered outside and a riot ensued, involving lots of Sawyer's neighbours who disliked him intensely. He claimed in the Court of the Star Chamber that his own son, also Richard, had caused the riot along with Sir Francis. The outcome of the case is unknown. The Sawyers were Royalists during the Civil War. Edward Sawyer served with the King in Oxford. Didcot was severely affected by the many troops marching through the area at the time. In May 1644, the main contingent of Royalist cavalry were quartered in the village, followed by Parliamentary soldiers shortly after they left.

In 1841, the Great Western Railway arrived in Didcot when the line from London and Reading to Bristol was laid through the parish, because the landowners around Newbury prevented it from taking the more direct route. Abingdon, under the influence of Lord Wantage, was also opposed to the railway in its early years. So Didcot gained tremendously from such backward thinking communities when the station was built just east of the village. 'Dudcote Junction' with its locomotive depot became an important cross over point with the Oxford, Worcester and Wolverhampton Railway and Didcot quickly began to expand. Another route to Newbury and Southampton was later added and, during the Second World War, Army and RAF ordnance depots were built on the site of the present Didcot Power Station (which is in Sutton Courtenay despite its name) and Milton Trading Estate. These made Didcot Station an important centre for military logistics during the Western front Campaign and the build up to D-Day. All the depots are now gone, but  that for the locomotives became the Didcot Railway Centre in 1967. The station is, of course, now known as Didcot Parkway.

Largely based on the work of B F Lingham (2005).