Human settlements existed in Termoli since pre-historical times, as showed by the presence of ancient necropolises. The Romans patricians had villae in the nearby coast.
The first documentation of today's city dates to the presence of the ancestor of the current cathedral, documented in the 10th century. Termoli was a Lombard county until the arrival of the Normans, under which flourished and expanded. Later devastations meant a period of decay which lasted until around 1770, when the local nobles were permitted by the Kings of Naples to build new edifices along the coast and in direction of the countryside.
During World War II Termoli became the centre of one of the larger tank battles of the Italian campaign over the period October 2 to October 6, 1943. On the night of October 2/3, during Operation Devon, British Commandos of the 2nd Special Service Brigade, which comprised No. 3 (Army) Commando, 40 (Royal Marine) Commando and the Special Raiding Squadron landed by sea then cleared the town of most of its German defenders. During the first day these forces set up road blocks around the town and were joined by British infantry advancing across the Biferno river to the south-east. They were unaware that the 16th Panzer Division was on its way to create a new defensive line. On October 4 British reinforcements arrived by sea and land, but tanks were unable to cross the river until engineers completed a bridge for heavy traffic. On October 5 the panzers attacked, pushing much of the British line back in disarray. At the end of the day they were only a short distance from the town. However, further reinforcements arrived at the port, and the engineers completed their bridge allowing tanks to cross. On October 6 the Germans renewed their attack, but it soon stalled and the British, with Canadian tanks from the Three Rivers Regiment (12e Régiment blindé du Canada) in support, counter-attacked. They were successful and by October 7 the Germans were pulling back to their next line of defence.
Termoli is rapidly becoming one of the most important centres in the Molise. The latter region suffered from depopulation in the years after World War II and there has been a migration from the internal hill towns to the coastal resort. Its status as the pre-eminent resort site is now being challenged by Campomarino, about five kilometres (3.1 mi) southward.
The old town has been well restored. It is a genuine walled community jutting out into the sea. Many of the houses have been re-built and painted in a range of pastel colours. In a central square there is the cathedral (12th-13th century), dedicated to St. Mary of the Purification: it is a noteworthy example of Apulian Romanesque architecture which houses the relics of the two city's patron saints, Bassus of Lucera (San Basso) and Timothy. The upper part of the façade was destroyed by an earthquake in 1456, and also suffered from the Turkish sack of the city in 1566. The Baroque additions were eliminated in the restoration of 1930–69, returning the edifice to its original appearance. Part of a pre-existing basilica, built in the 11th century (over the original, smaller cathedral called Ecclesia Sanctae Mater) but soon destroyed, has been found under the edifice.
The Castle is the most pre-eminent structure in Termoli: erected by count Robert I of Loritello during the Norman domination (11th century), it was largely renovated during the rule of Frederick II (1240), after the damage created by an attack of the Venetian fleet. The Castle was part of a wider fortification system, including a wall surrounding the entire city, of which only a tower can still be seen.
Termoli's resorts are renowned for the quality of their beaches and the relative purity of their waters.
Very few non-Italians come to stay in this area. Increasingly, the tourists to Molise are from the Naples and Apulia regions, to the south of Molise. Recently palm trees have been planted along the seaside promenade, and in the summer the many restaurants are crowded with visitors from surrounding communities.
Within a radius of about 25 kilometres (16 mi) from Termoli travellers can find the hilltowns of Larino, Casacalenda, Montorio, and Montelongo, which preserve a rural way of life which is disappearing in other, more developed, parts of Italy.
Termoli continues to be a port and a fishing town. A distinguishing feature of the old town are the trabucchi, wooden structures for fishing without the use of boats.
Ferries run from Termoli to the Isole Tremiti archipelago in the Adriatic Sea.
Termoli hosts several cultural events.
The Kimera Film Festival was established in 2003. Starting from 2008, the public selection of the short movies is held in Termoli, from February to April of every year.
Termoli was also the location of the Jamaican Dancehall video "Come inside" by Spice
Termoli is twinned with: Chorzów, Poland