Velletri was an important centre of the Volsci defeated by the Roman King Anco Marzio. From this area comes Gens Octavia, the family of the emperor Octavian Augustus.

Since the Middle Ages Velletri was one of the few free communes of Italy and, albeit with ups and downs, has always directed its own city life until 1591. In 1798 Velletri proclaimed a republic following the example of Rome, which had proclaimed the Roman Republic .

Technology arrived in the second half of the 1800s with one of the first telegraphs, the Rome-Velletri railway and the first banking institution in the modern sense, the Savings Bank of Velletri.

In 1806, an earthquake with its epicenter in Velletri virtually destroyed the city but there were no deaths and this is why the people of Velletri celebrate the Feast of Our Lady of Grace.

Velletri was at the centre of the Caesar line during WWII and was substantially heavily damaged when the Americans breached the German defences.