The parish of Haa was established as a municipality on 1 January 1838 (see formannskapsdistrikt). In 1894, the municipality of Haa was dissolved and divided into two new municipalities: Nærbø (population: 1,806) and Varhaug (population: 1,801). In the 1960s, there were many municipal mergers due to the work of the Schei Committee. On 1 January 1964, the municipality of Hå was recreated by merging of the neighboring municipalities of Nærbø (population: 3,926), Varhaug (population: 3,454), and Ogna (population: 1,470). In local politics, the divisions between the three previous municipalities are very visible.

The municipality is named after the old Hå farm (Old Norse: Háar) where the local church priest's parsonage was located. The meaning of the name is unknown. The river running past this farm is similarly named the Hååna, meaning the "Hå river". It is not known if the river is named after the farm or vice versa.

The coat-of-arms is from modern times; they were granted on 5 July 1991. The arms are black with a silver/white winch in the centre. It is a special type of winch that has historically been used in this area to remove stones from the many farm fields. The arms were chosen to symbolize the hard living on the rocky soils of the municipality.

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