Brønnøysund was separated from Brønnøy as a town (ladested), and municipality of its own, in 1923. 1 January 1964 it was again merged with neighbouring municipalities Sømna and Velfjord forming Brønnøy - and it then lost its status as a town until 2000. In 1977 Sømna separated into a municipality of its own. During the Viking era, Torgar, by the foot of the legendary mountain Torghatten, was a nationally powerful chieftain seat and an important commercial center along the coast. The original inhabitants were wiped out in an outright massacre by Duke Skule and his men in the Norwegian civil wars that raged around 1240, in the high medieval era of Norway.

The region was repopulated by immigrants from southern Norway, Trøndelag and Sweden, which could explain the unique dialect with a Swedish-like intonation.

Today Brønnøysund has approximately 5,000 inhabitants, and it is the administrative and commercial centre of the municipality of Brønnøy. A new township was declared in 2000. Brønnøysund has daily visits by the Hurtigruten (Coastal Express), northbound at night and southbound in the afternoon. It has its own airport, Brønnøysund Airport, Brønnøy, and a direct eastbound connection to the E6 highway. Throughout Norway the town is known as the location of the Brønnøysund Register Centre and Creditinform are the main commercial spin-offs of this register, in which the new e-government portal Altinn is the newest addition. Torghatten ASA has its headquarter in Brønnøysund.

In recent years, Brønnøysund has managed to create a certain economic growth. Fjord Seafood originated here, as well as the largest limestone mine in Northern Europe and the highest foodstuff production in Northern Norway are examples of entrepreneurship and well-run economy in this somewhat prosperous region. Additionally, there is a local heliport and an airport, but oddly the authorities had removed the direct flight to the national capital, Oslo, which is causing delays to Norwegian flows of documentation.

Modern agriculture, hydroponics, the large TTS transport corporation, wood-processing and tourism are the main driving industries.