The history of Calbayog is rooted in the early 17th century. Initially, a small settlement known as Tiayban existed in this territory along the riverbank. Jesuit missionaries, who arrived on Samar Island to spread Christianity and establish new communities, played an important role in the formation of the future city.
The establishment of Calbayog as an administrative unit occurred gradually. For a long time, it remained a dependent settlement attached to the mission of neighbouring Capul. It was only towards the end of the 18th century, in 1785, that Calbayog gained the status of an independent parish, which served as the starting point for its further growth and development.
The transformation of the small settlement into an important urban centre was driven by several strategic factors. Its location on the western coast of Samar Island provided convenient access to the sea, whilst the river network facilitated internal communication. In the 19th century, thanks to high global demand for abaca (Manila hemp), the region experienced a true economic boom. The development of the port allowed Calbayog to become the main trading gateway of Samar, through which goods were shipped to Manila and neighbouring islands.
The name of the city is shrouded in local legends. The most popular version suggests it originated from a misunderstanding between Spanish colonisers and a local resident. When asked for the name of the place, the resident, believing he was being asked about his activity, replied "naga-bayog" (transporting bayog wood down the river). Over time, this expression transformed into the modern name of the city. The economy of that time was built on a harmonious combination of agriculture and maritime trade, which shaped the unique commercial character of Calbayog.