A settlement was first established on the site of the old town almost 3000 years ago. From the 9th century BC and into the centuries that followed, Nin was a centre for trade with the Romans and Greeks; Roman villas have been discovered in the area, suggesting a prosperous and well-established trading community. Apart from its strategic significance, the town also prospered as a major source of salt.

Nin came under Croatian rule in the 7th century AD, and by 900 it was the seat of a Croatian bishop. It is also considered to have been the first Croatian royal town. It came under Venetian rule in 1409, and its strategic position was so important that the Venetians destroyed the town rather than abandon it to the Ottomans in 1571 and again in 1646.