Sorsogon City was created by virtue of Republic Act 8806, which was signed into law on August 16, 2000 and ratified during a plebiscite on December 16, 2000. RA 8806, also known as the Cityhood Law, called for the merger of the municipalities of Sorsogon and Bacon into a component city of the province of Sorsogon.

The merged municipalities of Bacon and Sorsogon more or less shared the same establishment pattern with Bacon leading the way. The present-day settlements grew out of the Spanish missionary efforts in the 1600s. They both started as missions that were later made into parishes and eventually declared as civilian political units.

Both places were already settled when the Spanish missionaries came in the 1600s. Pre-historic artifacts found pointing to human habitation ranged from the 3,000-year old remains in a cave in Bacon and ancient burial sites dug upstream of rivers in Sorsogon.

Bacon was established as a mission in 1609 with Casiguran, the oldest town in Sorsogon Province and one of the oldest in Luzon, as the parochial center. It became a parish in 1617. Sorsogon in turn was a mission of the parish of Bacon. Sorsogon became an independent parish in 1628.

Bacon was established as a civilian political unit (pueblo civil) in 1754. Sorsogon, on the other hand, became a pueblo civil in 1864. Being under the province of Albay (then composed of what are now the provinces of Albay, Sorsogon and Masbate) trade and travel was by water transport through the Albay Gulf. Road building between the two towns was done in the 1840s when the original bridges along the road connecting them were constructed. At this time both towns had also enjoyed the prosperity brought by the abaca trade when world supply was dominated by the Philippines. In the 1850s Albay was the richest province in the country.

On October 17, 1894, the Spanish authorities organized Sorsogon province as an administrative unit independent from Albay, with the town of Sorsogon as its seat of government. The new province adopted the name of the town and has since been known as the Province of Sorsogon. With the secession, Bacon lost Rapu-rapu which became a town of Albay. By the turn of the century Bacon further lost some of its area when Prieto Diaz was created as a town from the areas of Bacon and the town of Gubat.

At the start of the American period Sorsogon being the administrative center of the province became host to the Sorsogon School of Arts and Trade (now Sorsogon State College) and Sorsogon High School (now Sorsogon National High School). Both of these institutions served Sorsogon and its neighboring towns.