The settlement of Westleigh is Saxon in origin. It featured in the Domesday Book of 1086 under the of Weslega: "Robert of Albemarle has a manor called Weslega, which Ulward held on the day on which King Edward was alive and dead… "The manor covered seven acres and contained 4 villains (feudal tenants with some land), 5 bordars ( cottagers who would often hire out their labour ) and 4 serfs ( unskilled labourers with no rights). It was situated in the Fremington Hundred.

By 1238 the spelling had been changed to Westlegh, and by 1288 to Westleghe. It is not known when the current spelling was adopted: in a map thought to be early 18th century, it is shown as Westley. In Benjamin Donn’s Map of Devon (1765), the name had changed to Weftleigh which, given the practice at that time of using an f instead of an s, is probably one of the earliest instances of the current spelling being used. Thomas Moule’s map of 1830 splits Westleigh into two words.

The history of Westleigh is closely linked with that of neighbouring Instow (spelt Inftow on Benjamin Donn’s map ), and to a lesser extent with the manor house of Tapeley Hall ( Tapeleia in the Domesday Book) and its squire. At one time, the village was almost entirely owned by the Tapeley Estate, where most of the villagers worked, and much of it still is.

There are tombs in the church yard to the Christie family ( of Glyndebourne fame), who have occupied Tapeley Hall since the early 20th century, and to their predecessors, the Clevlands (also spelt Cleoland and Cleveland). The writer of this brief history lives in the house originally provided for the head groom of Tapeley Hall.

The village has traditionally been an agricultural community, although there are records of coal mining there, and it was – at least in the 16th and 17th centuries – a wealthy one. For example, when Henry VIII was raising taxes for the war with France in 1524, 33 people from Westleigh had to pay tax, compared with 23 from Instow.

In 1667, when Charles II decided to raise money by taxing people on the number of their hearths, Westleigh had , more sizeable houses than Instow, including one house belonging to John Burry which had fourteen heaths. On the other hand, Instow had only 33 "paupers" – people with a single hearth, considered too poor to be taxed – whereas Westleigh had at least 45.

In the 1850s, when the population of the parish was 525, there were two blacksmiths, two millers, three boot and shoe makers, three masons, three carpenters, an innkeeper (when the inn was called the New Inn), a tailor, a shopkeeper, two butchers and two teachers. There was also a Wesleyan chapel, now a private dwelling.