Gradac was inhabited in the prehistoric period, as evidenced by numerous stone piles from the Bronze and Iron Ages. In ancient times in this area most probably could be found a Roman civitas Biston, which as a coastal center belonged to the colony Narona, an important Roman base on today's Croatian territory. In Gradac area in medieval time there was castle Lapčan or Labinac , which alludes to the emperor Constantine Porfyrogenet. Under its present name of the town it was first mentioned in 1649. It was named after the fortress from the 17th century, which was located on a hill above the church of Sv. Mihovil (St Michael). On the hill above Gradac today you can still find remains of the old tower from the 16th century. Around it still stands number of houses, which have typical features of architecture of this region.
When the danger from Turkish and pirate attacks passed, population began migrating to the lower area, closer to the sea. Strong earthquake in 1962 contributed to the fact that the last inhabitants of this mountain village left the village and moved closer to the sea.
In the center of Gradac on an elevated antique site Gradina is a new church of Sv.Mihovil (St Michael)built in 1852. In the church there are three marble altars with statues, of which the most interesting is old wooden statue of Sv. Roka. In the church there is also an old stone font .
At the foot of the mountains is a Baroque church of Sv. Ante (St. Anthony) and the cemetery. One of the oldest buildings in Gradac is the chapel of Sv. Paškal on the hill Plana.