Brønnøy is a municipality in Nordland county, Norway. It is part of the Helgeland region. The administrative and commercial centre is the town of Brønnøysund. A secondary centre is the village of Hommelstø. Other villages include Tosbotn, Lande, Trælnes, and Indreskomo.The Brønnøysund Register Centre is an important employer in Brønnøy. Also, one of the largest limestone mines in Northern Europe is located in the municipality. Brønnøysund Airport, Brønnøy is located near the town of Brønnøysund.
The municipality of Brønnøy was established on 1 January 1838 (see formannskapsdistrikt). On 1 October 1875 the eastern district (population: 1,162) was separated to become the new municipality of Velfjord. This left Brønnøy with 4,156 residents.
Then on 1 January 1901, the southwestern district (population: 2,731) was separated to become the new municipality of Vik (which later changed its name to Sømna). Brønnøy was then left with 3,440 inhabitants. On 1 January 1923 the large village of Brønnøysund (population: 948) was separated from Brønnøy to become a town (ladested).