Long before Tandag became what it is today-- the bustling capital town of Surigao del Sur -- it was inhabited by the Manobos and the Mamanwas who lived along the river banks under the leadership of Suba , their Chieftain. Suba was later converted into Christianity by Father Juan de la Encarnacion, a Spanish missionary.

After Legaspi’s final conquest to the Philippines particularly on 1609, the Spanish Government sent missionaries to subdue the hostile natives. One of these missionaries was Father Juan de la Vega who was assigned in Tandag. In an effort to establish a symbol of authority, Fr. dela Vega erected a stone fort and built a small settlement about a size of a football field enclosed by a stone wall. Out of this settlement rose the town of  Tandag which later  on became a center a faith.
            About this period, Tandag became a port of call to the Spanish Galleon that sailed along the southern part of Mindanao. Until today, it is generally believed that somewhere underneath the deep sea near Tandag’s twin Linongao Islands lies a sunken galleon.
            In 1650, Tandag became the capital town of Surigao or Caraga, then a district that covered the present provinces of Agusan, the two Surigaos and a part of Davao. As center of faith and capital town, Tandag was forfeited with cottas which were erected sometime in the 18th century, within the northern part of the town and near the old cemetery at the western side. These fortification served to protect the town from Moro raids.
            In several separate attacks between 1754 and 1767, the Moro pirates wrought havoc and destruction to Tandag. Father Jose Ducos, aJesuit from Iligan, came to rescue and rebuild Tandag from the ruins wrought by these moro raids. He establish the Tandag Garrison and restored the Tandag priory.  Although the Tandag fort somehow survived, part of it was demolished during the Second World War. Calamities like typhoons and earthquakes finished off what remained of it. This explains why no remains of these structures could be seen today.
            Real transformation was finally afforded to Tandag via Republic Act No. 2786, an act that created Surigao del Sur and whose salient measure made Tandag the capital and seat of the provincial government of Surigao del Sur. Republic Act No. 9392 converting the municipality of Tandag into a component city to be known as the CITY OF TANDAG.