The island was originally 503 acres (2.04 square kilometres) in size. During World War II, in 1942 it was enlarged by reclamation, and by absorbing Long Bird Island and Cooper's Island, to 650 acres (263.0 hectares), in order to allow room for a US military base (originally the US Army's Fort Bell/Kindley Field, operated jointly during the war with the British RAF). This was later renamed as Kindley Air Force Base and USNAS Bermuda, which occupied more than half the island's land under a 99-year lease.
The base was closed in 1995 and returned to Bermuda. Much of its facilities are used as part of L.F. Wade International Airport. Cooper's Island is now attached physically to southeast St. David's, although the two islands are still widely regarded as if they were separate entities.
The island was named by British colonists in honour of Saint David, the patron saint of Wales, as the similarly sized St. George's Island, to the north, had been named for the patron saint of England. The two islands are separated by two bodies of water - Ferry Reach in the south-west and St. George's Harbor in the north-east. St. David's is separated from the Bermudian mainland by the waters of Castle Harbor in the south, but is joined to it by road via The Causeway.
Notable features of the island include St. David's Head, Bermuda's easternmost point, and the nearby St. David's Battery, on Great Head (Great Head is the more prominent of two headlands that comprise St. David's Head); L.F. Wade International Airport; St. David's Lighthouse; and Annie's Bay on Cooper's Island.
St. David's Island is connected to the United States by an Atlantic fiber optic cable known as 360 Americas. 
As with the rest of Bermuda, the St. David's islanders were established from a diverse group of immigrants, beginning in the 17th century. These included indentured servants from England, Spanish-speaking Blacks from the West Indies, and Black African, Native American, Irish, and Scottish slaves. The last three groups were largely composed of prisoners-of-war and others who were deported by the English from their homelands in ethnic cleansing that followed wars of conquest. Although hundreds of Native American slaves were absorbed into the total population of Bermuda, some Bermudians have long referred to St. David's islanders (disparagingly) as 'Mohawks'. Only two Mohawk boys were recorded as having been imported to Bermuda following Dutch-Mohawk wars. To many English in the late 17th and 18th centuries, however, the Iroquoian-speaking Mohawk were the best-known Native American people, as they were a powerful tribe in eastern New York. Some English of the period referred to any Native American as a Mohawk.
Today, many St. David's islanders are proud to be called Mohawks. They are actively re-establishing links to the Wampanoag, Pequot and other Algonquian nations that contributed the most members to Bermuda's early settlement. Since the joining of the Island to the rest of Bermuda by the US Army in the 1940s, the former relative isolation of St. David's has ended. The subsequent influx of other Bermudians to what is seen as a more affordable part of Bermuda to buy property, which increased dramatically after the closure of NAS Bermuda in 1995, has eroded the unique character of the islands population. They were once distinguishable by accent and appearance.
St. David's Preschool and Primary School are both on the island.
Clearwater Middle School is also located on St. David's. It opened on September 6, 1997 in the former Roger B. Chaffee High School with 155 students, formerly from the St. George's Secondary School.