Tsu originally developed as a castle town. During the Edo era, it became a popular stopping point for travelers to Ise shrine, about 40 km to the southeast. The old city was founded on April 1, 1889. although it has been rebuilt since then and remains one of the region's principal cities.
The city of Tsu was subjected to Allied air raids during World War II.
On January 1, 2006, the city of Hisai, the towns of An?, Gein? and Kawage, and the village of Misato, all from Age District; and the towns of Hakusan, Ichishi and Karasu, and the village of Misugi from Ichishi District, were merged into Tsu. The city became the eighth prefectural capital city to form the new municipal organizationjoining Saitama, Shizuoka, Aomori, Toyama, Matsue, Yamaguchi, and Saga. As a result of the merger, the city became the second largest in Mie by population behind Yokkaichi, and became the largest in Mie by area ahead of Matsusaka.
The city has also been prone to tsunamis in the past. A sea-wall was built in order to disrupt a tsunami long enough to give people time to evacuate the area
