You cannot see the join between these two villages today but, in Saxon times, they were a little distance apart. Since that time, they have always been separate parishes and Brightwell is actually split in two by Sotwell running through the middle. The name of the greater neighbour was originally Beorht-Wille which may have meant 'Bertha’s Spring'. Bertha was the Saxon Goddess of sacred springs and the Moon, indicating this was a sacred pagan area. A more boring interpretation is 'bright spring'. It was sometimes called West Brightwell or Brightwell Episcopi to differentiate it from Brightwell Baldwin in Oxfordshire. Sotwell may mean 'South Town Spring'. Mackney, the southern portion of the parishes, means 'Macca's Island'. So the springs must have created a number of streams which cut this area off from the rest.

The Roman road from Silchester to Dorchester-on-Thames passed through the parish down Mackney Lane. The ford where this road crossed the River Thames is one of the traditional sites of the baptism, by St. Birinus, of King Cynegils of Wessex and a large proportion of his Court, in the presence of King Oswald of Northumbria. It was mostly a political rather than a devotional act, for Cynegils wished to forge an alliance with the Christian King Oswald. The latter would only agree, however, if Cynegils would give up his pagan ways and marry Oswald’s daughter. St. Birinus’ arrival on the scene was merely opportune. King Cynegils gave Dorchester to Birinus so he could build himself a church (or cathedral) within the old Roman walls. These were the beginnings of the See of Wessex. Birinus became its first Bishop and remained so until his death in AD 649. His shrine at Dorchester became a great place of pilgrimage, but controversy later arose when the Bishop moved his seat to Winchester and claimed to have taken the body of Birinus with him.

In the 1150s, King Stephen built himself an early castle, at Brightwell, where the Georgian manor house now stands. Civil War was raging as he fought with his cousin, the Empress Matilda, for control of the country. The lady had her HQ at nearby Wallingford Castle, so Stephen put her under siege from a ring of fortifications. This site appears to have been chosen because the King’s brother, the Bishop of Winchester, Prince Henry of Blois, owned the manor and thought that Stephen could protect his estate and attack the Empress at the same time, thus killing two birds with one stone. The enclosing banks and ditches also surround the ancient parish church and it is therefore thought that it was originally erected by the Bishop as a garrison-church. He may have wanted to make the place a permanent counterpart to Wallingford. Though it was, in fact, destroyed by the Empress’ son in 1153. The church’s unusual dedication to St. Agatha is thought to indicate that it held one of her relics, possibly one of those collected by Henry in Rome and known to have been brought back to Winchester. The church does still house a number of good brasses. That showing the curate, John Schofield, as a priest holding the host: the only example in Berkshire. One Robert Ford of East Hendred murdered this poor man on the altar steps in 1507, by stabbing him in the head. The assailant then escaped by fleeing over the Thames! Another shows Robert Court and his wife, two years later. He lived at Mackney Court and was Auditor to Arthur, the ill-fated Prince of Wales. His Royal master is said to have visited him several times, during which Sotwell House, a Tudor building with a surviving moat, was put at his disposal. Other interesting buildings include the stone Elizabethan 'Small’s House' at Mackney - until the late 20th century owned by New College, Oxford - which was probably part of a late 'palace' for the Bishops of Winchester but is named after Burgess Small of Wallingford who built most of what can be seen today; and Priory Farm and Abbot’s House in Sotwell which were part of Wallingford Priory's holding in the village. Sotwell also has its own church. Rebuilt in 1884, it retains a few 12th and 14th century features.

The best known son of Brightwell is Sir Francis Bernard, a son of the local rector, who was born here in 1712. He studied to become a lawyer and went on to be Governor of New Jersey in 1758. In this office, he helped to enforce the measures which eventually led to the American Revolution. He was recalled in 1769 and rewarded with a baronetcy. Many of the Rectors of Brightwell were very minor celebrities: Thomas Brightwell, the Chancellor Oxford University who suffered as a Wycliffite; Thomas Goodwin, Master of Abingdon School, classical & theological writer (d. 1642); Edward Hyde, a Royalist divine deprived of his living;  John Ley, a member of the Westminster Assembly; Edward Bernard, astronomer and orientalist (d. 1697); Anthony Alsop a poetic writer (drowned 1727); and Thomas Wintle, a celebrated Hebraist (d.1814).